Metal enrichment by radiation pressure in active galactic nucleus outflows -- theory and observations. (arXiv:1207.7038v1 [astro-ph.CO]):
Outflows from active galactic nuclei may be produced by absorption of
continuum radiation by UV resonance lines of abundant metal ions, as observed
in broad absorption line quasars (BALQs). The radiation pressure exerted on the
metal ions is coupled to the rest of the gas through Coulomb collisions of the
metal ions. We calculate the photon density and gas density which allow
decoupling of the metal ions from the rest of the gas. These conditions may
lead to an outflow composed mostly of the metal ions. We derive a method to
constrain the metals/H ratio of observed UV outflows, based on the Ly {\alpha}
and Si iv {\lambda}{\lambda}1394, 1403 absorption profiles. We apply this
method to an SDSS sample of BALQs to derive a handful of candidate outflows
with a higher than solar metal/H ratio. This mechanism can produce ultra fast
UV outflows, if a shield of the continuum source with a strong absorption edge
is present.
Tuesday, July 31, 2012
Galactic Center Research: Manifestations of the Central Black Hole. (arXiv:1207.6755v1 [astro-ph.GA])
Galactic Center Research: Manifestations of the Central Black Hole. (arXiv:1207.6755v1 [astro-ph.GA]):
This review summarizes a few of the frontiers of Galactic center research
that are currently the focus of considerable activity and attention. It is
aimed at providing a necessarily incomplete sketch of some of the timely work
being done on phenomena taking place in, or originating in, the central few
parsecs of the Galaxy, with particular attention to topics related to the
Galactic black hole (GBH). We have chosen to expand on the following exciting
topics: 1) the characterization and the implications for the variability of
emission from the GBH, 2) the strong evidence for a powerful X-ray flare in the
Galactic center within the past few hundred years, and the likelihood that the
GBH is implicated in that event, 3) the prospects for detecting the "shadow" of
the GBH, 4) an overview of the current state of research on the central S-star
cluster, and what has been learned from the stellar orbits within that cluster,
and 5) the current hypotheses for the origin of the G2 dust cloud that is
projected to make a close passage by the GBH in 2013.
This review summarizes a few of the frontiers of Galactic center research
that are currently the focus of considerable activity and attention. It is
aimed at providing a necessarily incomplete sketch of some of the timely work
being done on phenomena taking place in, or originating in, the central few
parsecs of the Galaxy, with particular attention to topics related to the
Galactic black hole (GBH). We have chosen to expand on the following exciting
topics: 1) the characterization and the implications for the variability of
emission from the GBH, 2) the strong evidence for a powerful X-ray flare in the
Galactic center within the past few hundred years, and the likelihood that the
GBH is implicated in that event, 3) the prospects for detecting the "shadow" of
the GBH, 4) an overview of the current state of research on the central S-star
cluster, and what has been learned from the stellar orbits within that cluster,
and 5) the current hypotheses for the origin of the G2 dust cloud that is
projected to make a close passage by the GBH in 2013.
Sunday, July 29, 2012
On the Physics of Radio Halos in Galaxy Clusters: Scaling Relations and Luminosity Functions. (arXiv:1207.6410v1 [astro-ph.CO])
On the Physics of Radio Halos in Galaxy Clusters: Scaling Relations and Luminosity Functions. (arXiv:1207.6410v1 [astro-ph.CO]):
The underlying physics of giant radio halos and mini halos in galaxy clusters
is still an open question, which becomes more pressing with the growing number
of detections. In this paper, we explore the possibility that radio-emitting
electrons are generated in hadronic cosmic ray (CR) proton interactions with
ambient thermal protons of the intra-cluster medium. Our CR model derives from
cosmological hydrodynamical simulations of cluster formation and additionally
accounts for CR transport in the form of CR streaming and diffusion. This opens
the possibility of changing the radio halo luminosity by more than an order of
magnitude on a dynamical time scale. We build a mock galaxy cluster catalog
from the large MultiDark N-body LCDM simulation by adopting a phenomenological
gas density model for each cluster based on X-ray measurements that matches
Sunyaev-Zel'dovich (SZ) and X-ray scaling relations and luminosity function.
Using magnetic field strength estimates from Faraday rotation measure studies,
our model successfully reproduces the observed surface brightness profiles of
giant radio halos (Coma, A2163) as well as radio mini-halos (Perseus,
Ophiuchus), while obeying upper limits on the gamma-ray emission in these
clusters. Our model is also able to simultaneously reproduce the observed
bimodality of radio-loud and radio-quiet clusters at the same L_X as well as
the unimodal distribution of radio-halo luminosity versus the SZ flux Y;
thereby suggesting a physical solution to this apparent contradiction. For a
plausible fraction of 10% radio-loud clusters, our model matches the NVSS
radio-halo luminosity function. Constructing an analytical radio-halo
luminosity function, we demonstrate the unique prospects for low-frequency
radio surveys (such as the LOFAR Tier 1 survey) to detect ~3500 radio halos
back to redshift two and to probe the underlying physics of radio halos.
[abridged]
The underlying physics of giant radio halos and mini halos in galaxy clusters
is still an open question, which becomes more pressing with the growing number
of detections. In this paper, we explore the possibility that radio-emitting
electrons are generated in hadronic cosmic ray (CR) proton interactions with
ambient thermal protons of the intra-cluster medium. Our CR model derives from
cosmological hydrodynamical simulations of cluster formation and additionally
accounts for CR transport in the form of CR streaming and diffusion. This opens
the possibility of changing the radio halo luminosity by more than an order of
magnitude on a dynamical time scale. We build a mock galaxy cluster catalog
from the large MultiDark N-body LCDM simulation by adopting a phenomenological
gas density model for each cluster based on X-ray measurements that matches
Sunyaev-Zel'dovich (SZ) and X-ray scaling relations and luminosity function.
Using magnetic field strength estimates from Faraday rotation measure studies,
our model successfully reproduces the observed surface brightness profiles of
giant radio halos (Coma, A2163) as well as radio mini-halos (Perseus,
Ophiuchus), while obeying upper limits on the gamma-ray emission in these
clusters. Our model is also able to simultaneously reproduce the observed
bimodality of radio-loud and radio-quiet clusters at the same L_X as well as
the unimodal distribution of radio-halo luminosity versus the SZ flux Y;
thereby suggesting a physical solution to this apparent contradiction. For a
plausible fraction of 10% radio-loud clusters, our model matches the NVSS
radio-halo luminosity function. Constructing an analytical radio-halo
luminosity function, we demonstrate the unique prospects for low-frequency
radio surveys (such as the LOFAR Tier 1 survey) to detect ~3500 radio halos
back to redshift two and to probe the underlying physics of radio halos.
[abridged]
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events. (arXiv:1207.6401v1 [astro-ph.CO])
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events. (arXiv:1207.6401v1 [astro-ph.CO]):
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of stellar tidal debris can become gravitationally bound to
the black hole and be subsequently accreted, leading to a bright
electromagnetic flare. In the Newtonian limit, this flare will have a light
curve that scales as t^-5/3 if the tidal debris has a flat distribution in
binding energy. We investigate the time dependence of the black-hole mass
accretion rate when tidal disruption occurs close enough the black hole that
relativistic effects are significant. We find that for orbits with pericenters
comparable to the radius of the marginally bound circular orbit, relativistic
effects can double the peak accretion rate and halve the time it takes to reach
this peak accretion rate. The accretion rate depends on both the magnitude of
the black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.
Note: LSST could detect multiple such events -- might provide limits, worth considering.
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of stellar tidal debris can become gravitationally bound to
the black hole and be subsequently accreted, leading to a bright
electromagnetic flare. In the Newtonian limit, this flare will have a light
curve that scales as t^-5/3 if the tidal debris has a flat distribution in
binding energy. We investigate the time dependence of the black-hole mass
accretion rate when tidal disruption occurs close enough the black hole that
relativistic effects are significant. We find that for orbits with pericenters
comparable to the radius of the marginally bound circular orbit, relativistic
effects can double the peak accretion rate and halve the time it takes to reach
this peak accretion rate. The accretion rate depends on both the magnitude of
the black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.
Note: LSST could detect multiple such events -- might provide limits, worth considering.
Friday, July 27, 2012
Obscuration of Supersoft X-ray Sources by Circumbinary Material - A Way to Hide Type Ia Supernova Progenitors?. (arXiv:1207.6310v1 [astro-ph.SR])
Obscuration of Supersoft X-ray Sources by Circumbinary Material - A Way to Hide Type Ia Supernova Progenitors?. (arXiv:1207.6310v1 [astro-ph.SR]):
The progenitors of supernovae (SNe) type Ia are usually assumed to be either
a single white dwarf (WD) accreting from a non-degenerate companion (the SD
channel) or the result of two merging WDs (DD channel). However, no consensus
currently exists as to which progenitor scenario is the correct one, or whether
the observed SN Ia rate is produced by a combination of both channels. Unlike a
DD progenitor a SD progenitor is expected to emit supersoft X-rays for a
prolonged period of time (~1 Myr) as a result of the burning of accreted matter
on the surface of the WD. An argument against the SD channel as a significant
producer of SNe type Ia has been the lack of observed supersoft X-ray sources
(SSS) and the lower-than-expected integrated soft X-ray flux from elliptical
galaxies.
We wish to determine if it is possible to obscure the supersoft X-ray
emission from a nuclear burning white dwarf in an accreting single degenerate
binary system. In case of obscured systems we wish to determine their general
observational characteristics.
We examine the emergent X-ray emission from a canonical SSS system surrounded
by a spherically symmetric configuration of material, assuming a black body
spectrum with T_BB=50 eV and L=10^38 erg/s. The circumbinary material is
assumed to be of solar chemical abundances, and we leave the mechanism behind
the mass loss into the circumbinary region unspecified.
If steadily accreting, nuclear burning WDs are canonical SSS our analysis
suggests that they can be obscured by relatively modest circumbinary mass loss
rates. This may explain the discrepancy of SSS compared to the SN Ia rate
inferred from observations if the SD progenitor scenario contributes
significantly to the SN Ia rate. Recycled emissions from obscured systems may
be visible in other wavebands than X-rays. It may also explain the lack of
observed SSS in symbiotic binary systems.
The progenitors of supernovae (SNe) type Ia are usually assumed to be either
a single white dwarf (WD) accreting from a non-degenerate companion (the SD
channel) or the result of two merging WDs (DD channel). However, no consensus
currently exists as to which progenitor scenario is the correct one, or whether
the observed SN Ia rate is produced by a combination of both channels. Unlike a
DD progenitor a SD progenitor is expected to emit supersoft X-rays for a
prolonged period of time (~1 Myr) as a result of the burning of accreted matter
on the surface of the WD. An argument against the SD channel as a significant
producer of SNe type Ia has been the lack of observed supersoft X-ray sources
(SSS) and the lower-than-expected integrated soft X-ray flux from elliptical
galaxies.
We wish to determine if it is possible to obscure the supersoft X-ray
emission from a nuclear burning white dwarf in an accreting single degenerate
binary system. In case of obscured systems we wish to determine their general
observational characteristics.
We examine the emergent X-ray emission from a canonical SSS system surrounded
by a spherically symmetric configuration of material, assuming a black body
spectrum with T_BB=50 eV and L=10^38 erg/s. The circumbinary material is
assumed to be of solar chemical abundances, and we leave the mechanism behind
the mass loss into the circumbinary region unspecified.
If steadily accreting, nuclear burning WDs are canonical SSS our analysis
suggests that they can be obscured by relatively modest circumbinary mass loss
rates. This may explain the discrepancy of SSS compared to the SN Ia rate
inferred from observations if the SD progenitor scenario contributes
significantly to the SN Ia rate. Recycled emissions from obscured systems may
be visible in other wavebands than X-rays. It may also explain the lack of
observed SSS in symbiotic binary systems.
Thursday, July 26, 2012
Black Hole-Neutron Star Mergers: Disk Mass Predictions. (arXiv:1207.6304v1 [astro-ph.HE])
Black Hole-Neutron Star Mergers: Disk Mass Predictions. (arXiv:1207.6304v1 [astro-ph.HE]):
Determining the final result of black hole-neutron star mergers, and in
particular the amount of matter remaining outside the black hole at late times,
has been one of the main motivations behind the numerical simulation of these
systems. Black hole-neutron star binaries are amongst the most likely
progenitors of short gamma-ray bursts --- as long as they result in the
formation of massive (at least ~0.1 solar mass) accretion disks around the
black hole. Whether this actually happens strongly depends on the physical
characteristics of the system, and in particular on the mass ratio, the spin of
the black hole, and the radius of the neutron star. We present here a simple
two-parameter model, fitted to existing numerical results, for the
determination of the mass remaining outside the black hole a few milliseconds
after a black hole-neutron star merger. This model predicts the remnant mass
within a few percents of the mass of the neutron star, at least for remnant
masses up to 20% of the neutron star mass. Results across the range of
parameters deemed to be the most likely astrophysically are presented here. We
find that, for 10 solar mass black holes, massive disks are only possible for
fairly large neutron stars (R>12km), or quasi-extremal black hole spins
(a/M>0.9). We also use our model to discuss how the equation of state of the
neutron star affects the final remnant, and the strong influence that this can
have on the rate of short gamma-ray bursts produced by black hole-neutron star
mergers.
Determining the final result of black hole-neutron star mergers, and in
particular the amount of matter remaining outside the black hole at late times,
has been one of the main motivations behind the numerical simulation of these
systems. Black hole-neutron star binaries are amongst the most likely
progenitors of short gamma-ray bursts --- as long as they result in the
formation of massive (at least ~0.1 solar mass) accretion disks around the
black hole. Whether this actually happens strongly depends on the physical
characteristics of the system, and in particular on the mass ratio, the spin of
the black hole, and the radius of the neutron star. We present here a simple
two-parameter model, fitted to existing numerical results, for the
determination of the mass remaining outside the black hole a few milliseconds
after a black hole-neutron star merger. This model predicts the remnant mass
within a few percents of the mass of the neutron star, at least for remnant
masses up to 20% of the neutron star mass. Results across the range of
parameters deemed to be the most likely astrophysically are presented here. We
find that, for 10 solar mass black holes, massive disks are only possible for
fairly large neutron stars (R>12km), or quasi-extremal black hole spins
(a/M>0.9). We also use our model to discuss how the equation of state of the
neutron star affects the final remnant, and the strong influence that this can
have on the rate of short gamma-ray bursts produced by black hole-neutron star
mergers.
An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO])
An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger. (arXiv:1207.6235v1 [astro-ph.CO]):
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......
RKS Note: Background AGN behind a Galaxy Cluster...
We investigate the physical properties, geometry and dynamics of the massive
cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics.
Featuring two galaxy overdensities separated by about 250 kpc in projection on
the sky, and a single peak in the X-ray surface brightness distribution located
between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of
a binary, post-collision merger. Our spectral analysis of the X-ray emission,
as measured by our Chandra ACIS-I observation of the system, finds the
intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs
of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field
of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s
(n_z=66) and no significant evidence of bimodality or substructure along the
line of sight. In addition, the difference in radial velocity between the
brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small
compared to typical collision velocities of several 1000 km/s. A strongly
lensed background galaxy at z=0.873 (which features variable X-ray emission
from an active nucleus) provides the main constraint on the mass distribution
of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the
north-western cluster component and a much less certain estimate of
(1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good
agreement with our X-ray mass estimates which yield a total mass of MACS
J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......
RKS Note: Background AGN behind a Galaxy Cluster...
Theoretical Uncertainties due to AGN Subgrid Models in Predictions of Galaxy Cluster Observable Properties. (arXiv:1207.6106v1 [astro-ph.CO])
Theoretical Uncertainties due to AGN Subgrid Models in Predictions of Galaxy Cluster Observable Properties. (arXiv:1207.6106v1 [astro-ph.CO]):
Cosmological constraints derived from galaxy clusters rely on accurate
predictions of cluster observable properties, in which feedback from active
galactic nuclei (AGN) is a critical component. In order to model the physical
effects due to supermassive black holes (SMBH) on cosmological scales, subgrid
modeling is required, and a variety of implementations have been developed in
the literature. However, theoretical uncertainties due to model and parameter
variations are not yet well understood, limiting the predictive power of
simulations including AGN feedback. By performing a detailed parameter
sensitivity study in a single cluster using several commonly-adopted AGN
accretion and feedback models with FLASH, we quantify the model uncertainties
in predictions of cluster integrated properties. We find that quantities that
are more sensitive to gas density have larger uncertainties (~20% for Mgas and
a factor of ~2 for Lx at R500), whereas Tx, Ysz, and Yx are more robust
(~10-20% at R500). To make predictions beyond this level of accuracy would
require more constraints on the most relevant parameters: the accretion model,
mechanical heating efficiency, and size of feedback region. By studying the
impact of AGN feedback on the scaling relations, we find that an
anti-correlation exists between Mgas and Tx, which is another reason why Ysz
and Yx are excellent mass proxies. This anti-correlation also implies that AGN
feedback is likely to be an important source of intrinsic scatter in the
Mgas-Tx and Lx-Tx relations.
Cosmological constraints derived from galaxy clusters rely on accurate
predictions of cluster observable properties, in which feedback from active
galactic nuclei (AGN) is a critical component. In order to model the physical
effects due to supermassive black holes (SMBH) on cosmological scales, subgrid
modeling is required, and a variety of implementations have been developed in
the literature. However, theoretical uncertainties due to model and parameter
variations are not yet well understood, limiting the predictive power of
simulations including AGN feedback. By performing a detailed parameter
sensitivity study in a single cluster using several commonly-adopted AGN
accretion and feedback models with FLASH, we quantify the model uncertainties
in predictions of cluster integrated properties. We find that quantities that
are more sensitive to gas density have larger uncertainties (~20% for Mgas and
a factor of ~2 for Lx at R500), whereas Tx, Ysz, and Yx are more robust
(~10-20% at R500). To make predictions beyond this level of accuracy would
require more constraints on the most relevant parameters: the accretion model,
mechanical heating efficiency, and size of feedback region. By studying the
impact of AGN feedback on the scaling relations, we find that an
anti-correlation exists between Mgas and Tx, which is another reason why Ysz
and Yx are excellent mass proxies. This anti-correlation also implies that AGN
feedback is likely to be an important source of intrinsic scatter in the
Mgas-Tx and Lx-Tx relations.
Recent Progress on Developments and Characterization of Hybrid CMOS X-ray Detectors. (arXiv:1207.6058v1 [astro-ph.IM])
Recent Progress on Developments and Characterization of Hybrid CMOS X-ray Detectors. (arXiv:1207.6058v1 [astro-ph.IM]):
Future space-based X-ray telescope missions are likely to have significantly
increased demands on detector read out rates due to increased collection area,
and there will be a desire to minimize radiation damage in the interests of
maintaining spectral resolution. While CCDs have met the requirements of past
missions, active pixel sensors are likely to be a standard choice for some
future missions due to their inherent radiation hardness and fast, flexible
read-out architecture. One form of active pixel sensor is the hybrid CMOS
sensor. In a joint program of Penn State University and Teledyne Imaging
Sensors, hybrid CMOS sensors have been developed for use as X-ray detectors.
Results of this development effort and tests of fabricated detectors will be
presented, along with potential applications for future missions.
Future space-based X-ray telescope missions are likely to have significantly
increased demands on detector read out rates due to increased collection area,
and there will be a desire to minimize radiation damage in the interests of
maintaining spectral resolution. While CCDs have met the requirements of past
missions, active pixel sensors are likely to be a standard choice for some
future missions due to their inherent radiation hardness and fast, flexible
read-out architecture. One form of active pixel sensor is the hybrid CMOS
sensor. In a joint program of Penn State University and Teledyne Imaging
Sensors, hybrid CMOS sensors have been developed for use as X-ray detectors.
Results of this development effort and tests of fabricated detectors will be
presented, along with potential applications for future missions.
An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649. (arXiv:1207.5814v1 [astro-ph.CO])
An In-Depth Study of the Abundance Pattern in the Hot Interstellar Medium in NGC 4649. (arXiv:1207.5814v1 [astro-ph.CO]):
We present our X-ray imaging spectroscopic analysis of data from deep Suzaku
and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC
4649 (M60), focusing on the abundance pattern in the hot interstellar medium
(ISM). All measured elements show a radial decline in abundance, with the
possible exception of Oxygen. We construct steady state solutions to the
chemical evolution equations that include infall in addition to stellar mass
return and SNIa enrichment, and consider recently published SNIa yields. By
adjusting a single model parameter to obtain a match to the global abundance
pattern in NGC 4649 we infer that introduction of subsolar metallicity external
gas has reduced the overall ISM metallicity and diluted the effectiveness of
SNIa to skew the pattern towards low alpha-to-Fe ratios, and estimate the
combination of SNIa rate and level of dilution. Evidently, newly-introduced gas
is heated as it is integrated into, and interacts with, the hot gas that is
already present. These results indicate a complex flow and enrichment history
for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond
the formation epoch. The heating and circulation of accreted gas may help
reconcile this dynamic history with the mostly passive evolution of elliptical
stellar populations. In an appendix we examine the effects of the recent
updated atomic database AtomDB in spectral fitting of thermal plasmas with hot
ISM temperatures in the elliptical galaxy range.
We present our X-ray imaging spectroscopic analysis of data from deep Suzaku
and XMM-Newton Observatory exposures of the Virgo Cluster elliptical galaxy NGC
4649 (M60), focusing on the abundance pattern in the hot interstellar medium
(ISM). All measured elements show a radial decline in abundance, with the
possible exception of Oxygen. We construct steady state solutions to the
chemical evolution equations that include infall in addition to stellar mass
return and SNIa enrichment, and consider recently published SNIa yields. By
adjusting a single model parameter to obtain a match to the global abundance
pattern in NGC 4649 we infer that introduction of subsolar metallicity external
gas has reduced the overall ISM metallicity and diluted the effectiveness of
SNIa to skew the pattern towards low alpha-to-Fe ratios, and estimate the
combination of SNIa rate and level of dilution. Evidently, newly-introduced gas
is heated as it is integrated into, and interacts with, the hot gas that is
already present. These results indicate a complex flow and enrichment history
for NGC 4649, reflecting the continual evolution of elliptical galaxies beyond
the formation epoch. The heating and circulation of accreted gas may help
reconcile this dynamic history with the mostly passive evolution of elliptical
stellar populations. In an appendix we examine the effects of the recent
updated atomic database AtomDB in spectral fitting of thermal plasmas with hot
ISM temperatures in the elliptical galaxy range.
Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266. (arXiv:1207.5799v1 [astro-ph.CO])
Gemini GMOS and WHT SAURON integral-field spectrograph observations of the AGN driven outflow in NGC 1266. (arXiv:1207.5799v1 [astro-ph.CO]):
We use the SAURON and GMOS integral field spectrographs to observe the active
galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is
relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN
feedback in action. We present maps of the kinematics and line strengths of the
ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and
report on the detection of Sodium D absorption. We use these tracers to explore
the structure of the source, derive the ionised and atomic gas kinematics and
investigate the gas excitation and physical conditions. NGC 1266 contains two
ionised gas components along most lines of sight, tracing the ongoing outflow
and a component closer to the galaxy systemic, the origin of which is unclear.
This gas appears to be disturbed by a nascent AGN jet. We confirm that the
outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic,
molecular and ionised gas and X-ray emitting plasma. The outflow has velocities
up to \pm900 km/s away from the systemic velocity, and is very likely to be
removing significant amounts of cold gas from the galaxy. The LINER-like
line-emission in NGC 1266 is extended, and likely arises from fast shocks
caused by the interaction of the radio jet with the ISM. These shocks have
velocities of up to 800 km/s, which match well with the observed velocity of
the outflow. Sodium D equivalent width profiles are used to set constraints on
the size and orientation of the outflow. The ionised gas morphology correlates
with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission,
supporting the suggestion that an AGN jet is providing the energy required to
drive the outflow.
RKS Note: Introduction has nice two-paragraph description of the feedback problem.
We use the SAURON and GMOS integral field spectrographs to observe the active
galactic nucleus (AGN) powered outflow in NGC 1266. This unusual galaxy is
relatively nearby (D=30 Mpc), allowing us to investigate the process of AGN
feedback in action. We present maps of the kinematics and line strengths of the
ionised gas emission lines Halpha, Hbeta, [OIII], [OI], [NII] and [SII], and
report on the detection of Sodium D absorption. We use these tracers to explore
the structure of the source, derive the ionised and atomic gas kinematics and
investigate the gas excitation and physical conditions. NGC 1266 contains two
ionised gas components along most lines of sight, tracing the ongoing outflow
and a component closer to the galaxy systemic, the origin of which is unclear.
This gas appears to be disturbed by a nascent AGN jet. We confirm that the
outflow in NGC 1266 is truly multiphase, containing radio plasma, atomic,
molecular and ionised gas and X-ray emitting plasma. The outflow has velocities
up to \pm900 km/s away from the systemic velocity, and is very likely to be
removing significant amounts of cold gas from the galaxy. The LINER-like
line-emission in NGC 1266 is extended, and likely arises from fast shocks
caused by the interaction of the radio jet with the ISM. These shocks have
velocities of up to 800 km/s, which match well with the observed velocity of
the outflow. Sodium D equivalent width profiles are used to set constraints on
the size and orientation of the outflow. The ionised gas morphology correlates
with the nascent radio jets observed in 1.4 GHz and 5 GHz continuum emission,
supporting the suggestion that an AGN jet is providing the energy required to
drive the outflow.
RKS Note: Introduction has nice two-paragraph description of the feedback problem.
Wednesday, July 25, 2012
Recurrent radio outbursts at the center of the NGC1407 galaxy group. (arXiv:1206.5751v1 [astro-ph.CO])
Recurrent radio outbursts at the center of the NGC1407 galaxy group. (arXiv:1206.5751v1 [astro-ph.CO]):
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at
240, 330 and 610 MHz of the complex radio source at the center of the NGC1407
galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse
emission enclosing the central twin-jet radio galaxy. This has been interpreted
as an indication of two possible radio outbursts occurring at different times.
Both the inner double and diffuse component are detected in the new GMRT images
at high levels of significance. Combining the GMRT observations with archival
Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both
components. The inner double has a spectral index \alpha=0.7, typical for
active, extended radio galaxies, whereas the spectrum of the large-scale
emission is very steep, with \alpha=1.8 between 240 MHz and 1.4 GHz. The
radiative age of the large-scale component is very long, ~300 Myr, compared to
~30 Myr estimated for the central double, confirming that the diffuse component
was generated during a former cycle of activity of the central galaxy. The
current activity have so far released an energy which is nearly one order of
magnitude lower than that associated with the former outburst. The group X-ray
emission in the Chandra and XMM-Newton images and extended radio emission show
a similar swept-back morphology. We speculate that the two structures are both
affected by the motion of the group core, perhaps due to the core sloshing in
response to a recent encounter with the nearby elliptical galaxy NGC1400.
We present deep Giant Metrewave Radio Telescope (GMRT) radio observations at
240, 330 and 610 MHz of the complex radio source at the center of the NGC1407
galaxy group. Previous GMRT observations at 240 MHz revealed faint, diffuse
emission enclosing the central twin-jet radio galaxy. This has been interpreted
as an indication of two possible radio outbursts occurring at different times.
Both the inner double and diffuse component are detected in the new GMRT images
at high levels of significance. Combining the GMRT observations with archival
Very Large Array data at 1.4 and 4.9 GHz, we derive the total spectrum of both
components. The inner double has a spectral index \alpha=0.7, typical for
active, extended radio galaxies, whereas the spectrum of the large-scale
emission is very steep, with \alpha=1.8 between 240 MHz and 1.4 GHz. The
radiative age of the large-scale component is very long, ~300 Myr, compared to
~30 Myr estimated for the central double, confirming that the diffuse component
was generated during a former cycle of activity of the central galaxy. The
current activity have so far released an energy which is nearly one order of
magnitude lower than that associated with the former outburst. The group X-ray
emission in the Chandra and XMM-Newton images and extended radio emission show
a similar swept-back morphology. We speculate that the two structures are both
affected by the motion of the group core, perhaps due to the core sloshing in
response to a recent encounter with the nearby elliptical galaxy NGC1400.
The mystery of the missing GRB redshifts. (arXiv:1206.5558v1 [astro-ph.CO])
The mystery of the missing GRB redshifts. (arXiv:1206.5558v1 [astro-ph.CO]):
It is clear that optical selection effects have distorted the "true" GRB
redshift distribution to its presently observed biased distribution. We
constrain a statistically optimal model that implies GRB host galaxy dust
extinction could account for up to 40% of missing optical afterglows and
redshifts in $z = 0-3$, but the bias is negligible at very high-$z$. The
limiting sensitivity of the telescopes, and the time to acquire
spectroscopic/photometric redshifts, are significant sources of bias for the
very high-$z$ sample. We caution on constraining star formation rate and
luminosity evolution using the GRB redshift distribution without accounting for
these selection effects.
It is clear that optical selection effects have distorted the "true" GRB
redshift distribution to its presently observed biased distribution. We
constrain a statistically optimal model that implies GRB host galaxy dust
extinction could account for up to 40% of missing optical afterglows and
redshifts in $z = 0-3$, but the bias is negligible at very high-$z$. The
limiting sensitivity of the telescopes, and the time to acquire
spectroscopic/photometric redshifts, are significant sources of bias for the
very high-$z$ sample. We caution on constraining star formation rate and
luminosity evolution using the GRB redshift distribution without accounting for
these selection effects.
Demographics and Physical Properties of Gas Out/Inflows at 0.4 < z < 1.4. (arXiv:1206.5552v2 [astro-ph.CO] UPDATED)
Demographics and Physical Properties of Gas Out/Inflows at 0.4 < z < 1.4. (arXiv:1206.5552v2 [astro-ph.CO] UPDATED):
We present Keck/LRIS spectra of over 200 galaxies with well-determined
redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet,
low-ionization absorption lines with previously measured masses, luminosities,
colors, and star formation rates to describe the demographics and properties of
galactic flows. Among star-forming galaxies with blue colors, we find a net
blueshift of the Fe II absorption greater than 200 km/s (100 km/s) towards 2.5%
(20%) of the galaxies. The fraction of spectra with blueshifts decreases
significantly among galaxies with specific star formation rates less than
roughly 0.8 Gyr^{-1} and does not vary significantly with stellar mass, color,
or luminosity. The insensitivity of the blueshifted fraction to galaxy
properties favors collimated outflows, and in this context we demonstrate how
the solid angle of the outflow declines with increasing outflow velocity. We
also detect enriched infall towards 3-6% of the galaxies, apparently observed
at an optimal viewing angle. At least 3 (1) of the 9 infalling streams have a
large cross section and velocities commensurate with an extended disk
(satellite galaxy). We explain the strong dependence of the Mg II absorption
equivalent width on stellar mass, B-band luminosity, and U-B color by resonance
emission partially filling in the intrinsic absorption troughs; emission
filling can also explain the significant differences often observed between the
shape of the Mg II line profile and the absorption troughs of those Fe II
transitions that decay primarily by fluorescence. This study provides a new
quantitative understanding of gas flows between galaxies and the circumgalactic
medium over a critical period in galaxy evolution.
We present Keck/LRIS spectra of over 200 galaxies with well-determined
redshifts between 0.4 and 1.4. We combine new measurements of near-ultraviolet,
low-ionization absorption lines with previously measured masses, luminosities,
colors, and star formation rates to describe the demographics and properties of
galactic flows. Among star-forming galaxies with blue colors, we find a net
blueshift of the Fe II absorption greater than 200 km/s (100 km/s) towards 2.5%
(20%) of the galaxies. The fraction of spectra with blueshifts decreases
significantly among galaxies with specific star formation rates less than
roughly 0.8 Gyr^{-1} and does not vary significantly with stellar mass, color,
or luminosity. The insensitivity of the blueshifted fraction to galaxy
properties favors collimated outflows, and in this context we demonstrate how
the solid angle of the outflow declines with increasing outflow velocity. We
also detect enriched infall towards 3-6% of the galaxies, apparently observed
at an optimal viewing angle. At least 3 (1) of the 9 infalling streams have a
large cross section and velocities commensurate with an extended disk
(satellite galaxy). We explain the strong dependence of the Mg II absorption
equivalent width on stellar mass, B-band luminosity, and U-B color by resonance
emission partially filling in the intrinsic absorption troughs; emission
filling can also explain the significant differences often observed between the
shape of the Mg II line profile and the absorption troughs of those Fe II
transitions that decay primarily by fluorescence. This study provides a new
quantitative understanding of gas flows between galaxies and the circumgalactic
medium over a critical period in galaxy evolution.
Toward an accurate mass function for precision cosmology. (arXiv:1206.5302v1 [astro-ph.CO])
Toward an accurate mass function for precision cosmology. (arXiv:1206.5302v1 [astro-ph.CO]):
Cosmological surveys aim to use the evolution of the abundance of galaxy
clusters to accurately constrain the cosmological model. In the context of
LCDM, we show that it is possible to achieve the required percent level
accuracy in the halo mass function with gravity-only cosmological simulations,
and we provide simulation start and run parameter guidelines for doing so. Some
previous works have had sufficient statistical precision, but lacked robust
verification of absolute accuracy. Convergence tests of the mass function with,
for example, simulation start redshift can exhibit false convergence of the
mass function due to counteracting errors, potentially misleading one to infer
overly optimistic estimations of simulation accuracy. Percent level accuracy is
possible if initial condition particle mapping uses second order Lagrangian
Perturbation Theory, and if the start epoch is between 10 and 50 expansion
factors before the epoch of halo formation of interest. The mass function for
halos with fewer than ~1000 particles is highly sensitive to simulation
parameters and start redshift, implying a practical minimum mass resolution
limit due to mass discreteness. The narrow range in converged start redshift
suggests that it is not presently possible for a single simulation to capture
accurately the cluster mass function while also starting early enough to model
accurately the numbers of reionisation era galaxies, whose baryon feedback
processes may affect later cluster properties. Ultimately, to fully exploit
current and future cosmological surveys will require accurate modeling of
baryon physics and observable properties, a formidable challenge for which
accurate gravity-only simulations are just an initial step.
Cosmological surveys aim to use the evolution of the abundance of galaxy
clusters to accurately constrain the cosmological model. In the context of
LCDM, we show that it is possible to achieve the required percent level
accuracy in the halo mass function with gravity-only cosmological simulations,
and we provide simulation start and run parameter guidelines for doing so. Some
previous works have had sufficient statistical precision, but lacked robust
verification of absolute accuracy. Convergence tests of the mass function with,
for example, simulation start redshift can exhibit false convergence of the
mass function due to counteracting errors, potentially misleading one to infer
overly optimistic estimations of simulation accuracy. Percent level accuracy is
possible if initial condition particle mapping uses second order Lagrangian
Perturbation Theory, and if the start epoch is between 10 and 50 expansion
factors before the epoch of halo formation of interest. The mass function for
halos with fewer than ~1000 particles is highly sensitive to simulation
parameters and start redshift, implying a practical minimum mass resolution
limit due to mass discreteness. The narrow range in converged start redshift
suggests that it is not presently possible for a single simulation to capture
accurately the cluster mass function while also starting early enough to model
accurately the numbers of reionisation era galaxies, whose baryon feedback
processes may affect later cluster properties. Ultimately, to fully exploit
current and future cosmological surveys will require accurate modeling of
baryon physics and observable properties, a formidable challenge for which
accurate gravity-only simulations are just an initial step.
Suppressing hot gas accretion to supermassive black holes by stellar winds. (arXiv:1206.6029v1 [astro-ph.CO])
Suppressing hot gas accretion to supermassive black holes by stellar winds. (arXiv:1206.6029v1 [astro-ph.CO]):
We argue that one of the basic assumptions of the Bondi accretion process,
that the accreting object has zero pressure, might not hold in many galaxies
because of the pressure exerted by stellar winds of star orbiting the central
super massive black hole (SMBH). Hence, the Bondi accretion cannot be used in
these cases, such as in the galaxy NGC 3115. The winds of these high-velocity
stars are shocked to temperatures above the virial temperature of the galaxy,
leading to the formation of a hot bubble of size ~0.1-10 pc near the center.
This hot bubble can substantially reduce the mass accretion rate by the SMBH.
If the density of the hot bubble is lower than that of the interstellar medium
(ISM), a density-inversion layer is formed. Adding to other problems of the
Bondi process, our results render the Bondi accretion irrelevant for AGN
feedback in cooling flow in galaxies and small groups of galaxies and during
galaxy formation.
We argue that one of the basic assumptions of the Bondi accretion process,
that the accreting object has zero pressure, might not hold in many galaxies
because of the pressure exerted by stellar winds of star orbiting the central
super massive black hole (SMBH). Hence, the Bondi accretion cannot be used in
these cases, such as in the galaxy NGC 3115. The winds of these high-velocity
stars are shocked to temperatures above the virial temperature of the galaxy,
leading to the formation of a hot bubble of size ~0.1-10 pc near the center.
This hot bubble can substantially reduce the mass accretion rate by the SMBH.
If the density of the hot bubble is lower than that of the interstellar medium
(ISM), a density-inversion layer is formed. Adding to other problems of the
Bondi process, our results render the Bondi accretion irrelevant for AGN
feedback in cooling flow in galaxies and small groups of galaxies and during
galaxy formation.
Resonant Compton Upscattering in High Field Neutron Stars. (arXiv:1206.5957v1 [astro-ph.HE])
Resonant Compton Upscattering in High Field Neutron Stars. (arXiv:1206.5957v1 [astro-ph.HE]):
The extremely efficient process of resonant Compton upscattering by
relativistic electrons in high magnetic fields is believed to be a leading
emission mechanism of high field pulsars and magnetars in the production of
intense X-ray radiation. New analytic developments for the Compton scattering
cross section using Sokolov & Ternov (S&T) states with spin-dependent resonant
widths are presented. These new results display significant numerical
departures from both the traditional cross section using spin-averaged widths,
and also from the spin-dependent cross section that employs the Johnson &
Lippmann (J&L) basis states, thereby motivating the astrophysical deployment of
this updated resonant Compton formulation. Useful approximate analytic forms
for the cross section in the cyclotron resonance are developed for S&T basis
states. These calculations are applied to an inner magnetospheric model of the
hard X-ray spectral tails in magnetars, recently detected by RXTE and INTEGRAL.
Relativistic electrons cool rapidly near the stellar surface in the presence of
intense baths of thermal X-ray photons. We present resonant Compton cooling
rates for electrons, and the resulting photon spectra at various magnetospheric
locales, for magnetic fields above the quantum critical value. These
demonstrate how this scattering mechanism has the potential to produce the
characteristically flat spectral tails observed in magnetars.
The extremely efficient process of resonant Compton upscattering by
relativistic electrons in high magnetic fields is believed to be a leading
emission mechanism of high field pulsars and magnetars in the production of
intense X-ray radiation. New analytic developments for the Compton scattering
cross section using Sokolov & Ternov (S&T) states with spin-dependent resonant
widths are presented. These new results display significant numerical
departures from both the traditional cross section using spin-averaged widths,
and also from the spin-dependent cross section that employs the Johnson &
Lippmann (J&L) basis states, thereby motivating the astrophysical deployment of
this updated resonant Compton formulation. Useful approximate analytic forms
for the cross section in the cyclotron resonance are developed for S&T basis
states. These calculations are applied to an inner magnetospheric model of the
hard X-ray spectral tails in magnetars, recently detected by RXTE and INTEGRAL.
Relativistic electrons cool rapidly near the stellar surface in the presence of
intense baths of thermal X-ray photons. We present resonant Compton cooling
rates for electrons, and the resulting photon spectra at various magnetospheric
locales, for magnetic fields above the quantum critical value. These
demonstrate how this scattering mechanism has the potential to produce the
characteristically flat spectral tails observed in magnetars.
The Growth of the Stellar Seeds of Supermassive Black Holes. (arXiv:1206.5825v1 [astro-ph.CO])
The Growth of the Stellar Seeds of Supermassive Black Holes. (arXiv:1206.5825v1 [astro-ph.CO]):
One of the most promising explanations for the origin of the billion solar
mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that
supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form
the seed BHs from which they grow. Here we review recent theoretical advances
which provide support for this scenario. Firstly, given sufficiently high
accretion rates of gas into the cores of primordial protogalaxies, it appears
that neither the high energy radiation emitted from the stellar surface nor the
limited lifetime of SMSs can prevent their growth to masses of up to > 100,000
solar masses. Secondly, recent cosmological simulations suggest that the high
fluxes of molecule-dissociating radiation which may be required in order to
achieve such high accretion rates may be more common in the early universe than
previously thought. We conclude that the majority of supermassive BHs may
originate from SMSs at high redshifts.
One of the most promising explanations for the origin of the billion solar
mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that
supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form
the seed BHs from which they grow. Here we review recent theoretical advances
which provide support for this scenario. Firstly, given sufficiently high
accretion rates of gas into the cores of primordial protogalaxies, it appears
that neither the high energy radiation emitted from the stellar surface nor the
limited lifetime of SMSs can prevent their growth to masses of up to > 100,000
solar masses. Secondly, recent cosmological simulations suggest that the high
fluxes of molecule-dissociating radiation which may be required in order to
achieve such high accretion rates may be more common in the early universe than
previously thought. We conclude that the majority of supermassive BHs may
originate from SMSs at high redshifts.
Telescope Bibliographies: an Essential Component of Archival Data Management and Operations. (arXiv:1206.6352v1 [astro-ph.IM])
Telescope Bibliographies: an Essential Component of Archival Data Management and Operations. (arXiv:1206.6352v1 [astro-ph.IM]):
Assessing the impact of astronomical facilities rests upon an evaluation of
the scientific discoveries which their data have enabled. Telescope
bibliographies, which link data products with the literature, provide a way to
use bibliometrics as an impact measure for the underlying data. In this paper
we argue that the creation and maintenance of telescope bibliographies should
be considered an integral part of an observatory's operations. We review the
existing tools, services, and workflows which support these curation
activities, giving an estimate of the effort and expertise required to maintain
an archive-based telescope bibliography.
Assessing the impact of astronomical facilities rests upon an evaluation of
the scientific discoveries which their data have enabled. Telescope
bibliographies, which link data products with the literature, provide a way to
use bibliometrics as an impact measure for the underlying data. In this paper
we argue that the creation and maintenance of telescope bibliographies should
be considered an integral part of an observatory's operations. We review the
existing tools, services, and workflows which support these curation
activities, giving an estimate of the effort and expertise required to maintain
an archive-based telescope bibliography.
A parallax distance and mass estimate for the transitional millisecond pulsar system J1023+0038. (arXiv:1207.5670v1 [astro-ph.SR])
A parallax distance and mass estimate for the transitional millisecond pulsar system J1023+0038. (arXiv:1207.5670v1 [astro-ph.SR]):
The recently discovered transitional millisecond pulsar system J1023+0038
exposes a crucial evolutionary phase of recycled neutron stars for
multiwavelength study. The system, comprising the neutron star itself, its
stellar companion, and the surrounding medium, is visible across the
electromagnetic spectrum from the radio to X-ray/gamma-ray regimes and offers
insight into the recycling phase of millisecond pulsar evolution. Here, we
report on multiple-epoch astrometric observations with the Very Long Baseline
Array (VLBA) which give a system parallax of 0.731 +/- 0.022 milliarcseconds
(mas) and a proper motion of 17.98 +/- 0.05 mas/yr. By combining our results
with previous optical observations, we are able to use the parallax distance of
1368+42-39 pc to estimate the mass of the pulsar as 1.71 +/- 0.16 solar masses,
and we are also able to measure the 3D space velocity of the system as 126 +/-
5 km/s. Despite the precise nature of the VLBA measurements, the remaining ~3%
distance uncertainty dominates the 0.16 solar mass error on our mass estimate.
The recently discovered transitional millisecond pulsar system J1023+0038
exposes a crucial evolutionary phase of recycled neutron stars for
multiwavelength study. The system, comprising the neutron star itself, its
stellar companion, and the surrounding medium, is visible across the
electromagnetic spectrum from the radio to X-ray/gamma-ray regimes and offers
insight into the recycling phase of millisecond pulsar evolution. Here, we
report on multiple-epoch astrometric observations with the Very Long Baseline
Array (VLBA) which give a system parallax of 0.731 +/- 0.022 milliarcseconds
(mas) and a proper motion of 17.98 +/- 0.05 mas/yr. By combining our results
with previous optical observations, we are able to use the parallax distance of
1368+42-39 pc to estimate the mass of the pulsar as 1.71 +/- 0.16 solar masses,
and we are also able to measure the 3D space velocity of the system as 126 +/-
5 km/s. Despite the precise nature of the VLBA measurements, the remaining ~3%
distance uncertainty dominates the 0.16 solar mass error on our mass estimate.
The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole. (arXiv:1207.5657v1 [astro-ph.GA])
The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole. (arXiv:1207.5657v1 [astro-ph.GA]):
Star formation in the centers of galaxies is thought to yield massive stars
with a possibly top-heavy stellar mass distribution. It is likely that magnetic
fields play a crucial role in the distribution of stellar masses inside
star-forming molecular clouds. In this context, we explore the effects of
magnetic fields, with a typical field strength of 38 {\mu}G, such as in RCW 38,
and a field strength of 135 {\mu}G, similar to NGC 2024 and the infrared dark
cloud G28.34+0.06, on the initial mass function (IMF) near (\leq 10 pc) a 10^7
solar mass black hole. Using these conditions, we perform a series of numerical
simulations with the hydrodynamical code FLASH to elucidate the impact of
magnetic fields on the IMF and the star-formation efficiency (SFE) emerging
from an 800 solar mass cloud. We find that the collapse of a gravitationally
unstable molecular cloud is slowed down with increasing magnetic field strength
and that stars form along the field lines. The total number of stars formed
during the simulations increases by a factor of 1.5-2 with magnetic fields. The
main component of the IMF has a lognormal shape, with its peak shifted to
sub-solar (\leq 0.3 Mo) masses in the presence of magnetic fields, due to a
decrease in the accretion rates from the gas reservoir. In addition, we see a
top-heavy, nearly flat IMF above \sim 2 solar masses, from regions that were
supported by magnetic pressure until high masses are reached. We also consider
the effects of X-ray irradiation if the central black hole is active. X-ray
feedback inhibits the formation of sub-solar masses and decreases the SFEs even
further. Thus, the second contribution is no longer visible. We conclude that
magnetic fields potentially change the SFE and the IMF both in active and
inactive galaxies, and need to be taken into account in such calculations.
Star formation in the centers of galaxies is thought to yield massive stars
with a possibly top-heavy stellar mass distribution. It is likely that magnetic
fields play a crucial role in the distribution of stellar masses inside
star-forming molecular clouds. In this context, we explore the effects of
magnetic fields, with a typical field strength of 38 {\mu}G, such as in RCW 38,
and a field strength of 135 {\mu}G, similar to NGC 2024 and the infrared dark
cloud G28.34+0.06, on the initial mass function (IMF) near (\leq 10 pc) a 10^7
solar mass black hole. Using these conditions, we perform a series of numerical
simulations with the hydrodynamical code FLASH to elucidate the impact of
magnetic fields on the IMF and the star-formation efficiency (SFE) emerging
from an 800 solar mass cloud. We find that the collapse of a gravitationally
unstable molecular cloud is slowed down with increasing magnetic field strength
and that stars form along the field lines. The total number of stars formed
during the simulations increases by a factor of 1.5-2 with magnetic fields. The
main component of the IMF has a lognormal shape, with its peak shifted to
sub-solar (\leq 0.3 Mo) masses in the presence of magnetic fields, due to a
decrease in the accretion rates from the gas reservoir. In addition, we see a
top-heavy, nearly flat IMF above \sim 2 solar masses, from regions that were
supported by magnetic pressure until high masses are reached. We also consider
the effects of X-ray irradiation if the central black hole is active. X-ray
feedback inhibits the formation of sub-solar masses and decreases the SFEs even
further. Thus, the second contribution is no longer visible. We conclude that
magnetic fields potentially change the SFE and the IMF both in active and
inactive galaxies, and need to be taken into account in such calculations.
Principal components of dark energy with SNLS supernovae: the effects of systematic errors. (arXiv:1207.4781v1 [astro-ph.CO])
Principal components of dark energy with SNLS supernovae: the effects of systematic errors. (arXiv:1207.4781v1 [astro-ph.CO]):
We study the effects of current systematic errors in Type Ia supernova (SN
Ia) measurements on dark energy (DE) constraints using current data from the
Supernova Legacy Survey (SNLS). We consider how SN systematic errors affect
constraints from combined SN Ia, baryon acoustic oscillations (BAO), and cosmic
microwave background (CMB) data, given that SNe Ia still provide the strongest
constraints on DE but are arguably subject to more significant systematics than
the latter two probes. We focus our attention on the temporal evolution of DE
described in terms of principal components (PCs) of the equation of state,
though we examine a few of the more common, simpler parametrizations as well.
We find that the SN Ia systematics degrade the total generalized figure of
merit (FoM), which characterizes constraints in multi-dimensional DE parameter
space, by a factor of two to three. Nevertheless, overall constraints obtained
on more than five PCs are very good even with current data and systematics. We
further show that current constraints are robust to allowing for the finite
detection significance of the BAO feature in galaxy surveys.
We study the effects of current systematic errors in Type Ia supernova (SN
Ia) measurements on dark energy (DE) constraints using current data from the
Supernova Legacy Survey (SNLS). We consider how SN systematic errors affect
constraints from combined SN Ia, baryon acoustic oscillations (BAO), and cosmic
microwave background (CMB) data, given that SNe Ia still provide the strongest
constraints on DE but are arguably subject to more significant systematics than
the latter two probes. We focus our attention on the temporal evolution of DE
described in terms of principal components (PCs) of the equation of state,
though we examine a few of the more common, simpler parametrizations as well.
We find that the SN Ia systematics degrade the total generalized figure of
merit (FoM), which characterizes constraints in multi-dimensional DE parameter
space, by a factor of two to three. Nevertheless, overall constraints obtained
on more than five PCs are very good even with current data and systematics. We
further show that current constraints are robust to allowing for the finite
detection significance of the BAO feature in galaxy surveys.
Observing the dynamics of super-massive black hole binaries with Pulsar Timing Arrays. (arXiv:1207.5645v1 [astro-ph.HE])
Observing the dynamics of super-massive black hole binaries with Pulsar Timing Arrays. (arXiv:1207.5645v1 [astro-ph.HE]):
Pulsar Timing Arrays are a prime tool to study unexplored astrophysical
regimes with gravitational waves. Here we show that the detection of
gravitational radiation from individually resolvable super-massive black hole
binary systems can yield direct information about the masses and spins of the
black holes, provided that the gravitational-wave induced timing fluctuations
both at the pulsar and at the Earth are detected. This in turn provides a map
of the non-linear dynamics of the gravitational field and a new avenue to
tackle open problems in astrophysics connected to the formation and evolution
of super-massive black holes. We discuss the potential, the challenges and the
limitations of these observations.
Pulsar Timing Arrays are a prime tool to study unexplored astrophysical
regimes with gravitational waves. Here we show that the detection of
gravitational radiation from individually resolvable super-massive black hole
binary systems can yield direct information about the masses and spins of the
black holes, provided that the gravitational-wave induced timing fluctuations
both at the pulsar and at the Earth are detected. This in turn provides a map
of the non-linear dynamics of the gravitational field and a new avenue to
tackle open problems in astrophysics connected to the formation and evolution
of super-massive black holes. We discuss the potential, the challenges and the
limitations of these observations.
Impacts of The Radiation Environment At L2 On Bolometers Onboard The Herschel Space Observatory. (arXiv:1207.5597v1 [astro-ph.IM])
Impacts of The Radiation Environment At L2 On Bolometers Onboard The Herschel Space Observatory. (arXiv:1207.5597v1 [astro-ph.IM]):
We present the effects of cosmic rays on the detectors onboard the Herschel
satellite. We describe in particular the glitches observed on the two types of
cryogenic far- infrared bolometer inside the two instruments PACS and SPIRE.
The glitch rates are also reported since the launch together with the SREM
radiation monitors aboard Herschel and Planck spacecrafts. Both have been
injected around the Lagrangian point L2 on May 2009. This allows probing the
radiation environment around this orbit. The impacts on the observation are
finally summarized.
We present the effects of cosmic rays on the detectors onboard the Herschel
satellite. We describe in particular the glitches observed on the two types of
cryogenic far- infrared bolometer inside the two instruments PACS and SPIRE.
The glitch rates are also reported since the launch together with the SREM
radiation monitors aboard Herschel and Planck spacecrafts. Both have been
injected around the Lagrangian point L2 on May 2009. This allows probing the
radiation environment around this orbit. The impacts on the observation are
finally summarized.
Soft X-ray and ultra-violet metal-line emission from the gas around galaxies. (arXiv:1207.5512v1 [astro-ph.CO])
Soft X-ray and ultra-violet metal-line emission from the gas around galaxies. (arXiv:1207.5512v1 [astro-ph.CO]):
(Abridged) A large fraction of the gas in galactic haloes has temperatures
between 10^4.5 and 10^7 K. At these temperatures, cooling is dominated by
metal-line emission if the metallicity Z>~0.1 Zsun. We explore the
detectability of several lines using large cosmological, hydrodynamical
simulations. We stack surface brightness maps centred on galaxies to calculate
the expected mean surface brightness profiles for different halo masses.
Assuming a detection limit of 10^-1 photon s^-1 cm^-2 sr^-1, proposed X-ray
telescopes can detect O VIII emission from z=0.125 out to 80% of the virial
radius (Rvir) of groups and clusters and out to 0.4Rvir for haloes with masses
Mhalo=10^12-13 Msun. Emission lines from C VI, N VII, O VII, and Ne X can be
detected out to smaller radii, 0.1-0.5Rvir. With a detection limit of 10^-20
erg s^-1 cm^-2 arcsec^-2, future UV telescopes can detect C III emission out to
0.3-0.6Rvir at z=0.25. C IV, O VI, Si III, and Si IV can be seen out to
0.1-0.2Rvir for Mhalo>10^12 Msun. Optical HI H-alpha emission is comparable in
strength to C III emission. At z=3 it may be possible to observe C III out to
0.2-0.3Rvir and other rest-frame UV lines out to ~0.1Rvir for Mhalo>10^11 Msun
with upcoming optical instruments. Metal-line emission is typically biased
towards high density and metallicity and towards the temperature at which the
emissivity curve of the corresponding metal line peaks. The bias is similar for
the different soft X-ray lines considered, whereas it varies strongly between
different UV lines. Active galactic nucleus (AGN) feedback can change the inner
surface brightness profiles significantly, but it generally does not change the
radius out to which the emission can be observed. Metal-line emission is a
promising probe of the warm and hot, enriched gas around galaxies and provides
a unique window into the interactions between galaxies and their gaseous
haloes.
(Abridged) A large fraction of the gas in galactic haloes has temperatures
between 10^4.5 and 10^7 K. At these temperatures, cooling is dominated by
metal-line emission if the metallicity Z>~0.1 Zsun. We explore the
detectability of several lines using large cosmological, hydrodynamical
simulations. We stack surface brightness maps centred on galaxies to calculate
the expected mean surface brightness profiles for different halo masses.
Assuming a detection limit of 10^-1 photon s^-1 cm^-2 sr^-1, proposed X-ray
telescopes can detect O VIII emission from z=0.125 out to 80% of the virial
radius (Rvir) of groups and clusters and out to 0.4Rvir for haloes with masses
Mhalo=10^12-13 Msun. Emission lines from C VI, N VII, O VII, and Ne X can be
detected out to smaller radii, 0.1-0.5Rvir. With a detection limit of 10^-20
erg s^-1 cm^-2 arcsec^-2, future UV telescopes can detect C III emission out to
0.3-0.6Rvir at z=0.25. C IV, O VI, Si III, and Si IV can be seen out to
0.1-0.2Rvir for Mhalo>10^12 Msun. Optical HI H-alpha emission is comparable in
strength to C III emission. At z=3 it may be possible to observe C III out to
0.2-0.3Rvir and other rest-frame UV lines out to ~0.1Rvir for Mhalo>10^11 Msun
with upcoming optical instruments. Metal-line emission is typically biased
towards high density and metallicity and towards the temperature at which the
emissivity curve of the corresponding metal line peaks. The bias is similar for
the different soft X-ray lines considered, whereas it varies strongly between
different UV lines. Active galactic nucleus (AGN) feedback can change the inner
surface brightness profiles significantly, but it generally does not change the
radius out to which the emission can be observed. Metal-line emission is a
promising probe of the warm and hot, enriched gas around galaxies and provides
a unique window into the interactions between galaxies and their gaseous
haloes.
Tuesday, July 24, 2012
The Growth of the Stellar Seeds of Supermassive Black Holes. (arXiv:1206.5825v1 [astro-ph.CO])
The Growth of the Stellar Seeds of Supermassive Black Holes. (arXiv:1206.5825v1 [astro-ph.CO]):
One of the most promising explanations for the origin of the billion solar
mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that
supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form
the seed BHs from which they grow. Here we review recent theoretical advances
which provide support for this scenario. Firstly, given sufficiently high
accretion rates of gas into the cores of primordial protogalaxies, it appears
that neither the high energy radiation emitted from the stellar surface nor the
limited lifetime of SMSs can prevent their growth to masses of up to > 100,000
solar masses. Secondly, recent cosmological simulations suggest that the high
fluxes of molecule-dissociating radiation which may be required in order to
achieve such high accretion rates may be more common in the early universe than
previously thought. We conclude that the majority of supermassive BHs may
originate from SMSs at high redshifts.
One of the most promising explanations for the origin of the billion solar
mass black holes (BHs) inferred to power quasars at redshifts z > 6 is that
supermassive stars (SMSs) with masses > 10,000 solar masses collapse to form
the seed BHs from which they grow. Here we review recent theoretical advances
which provide support for this scenario. Firstly, given sufficiently high
accretion rates of gas into the cores of primordial protogalaxies, it appears
that neither the high energy radiation emitted from the stellar surface nor the
limited lifetime of SMSs can prevent their growth to masses of up to > 100,000
solar masses. Secondly, recent cosmological simulations suggest that the high
fluxes of molecule-dissociating radiation which may be required in order to
achieve such high accretion rates may be more common in the early universe than
previously thought. We conclude that the majority of supermassive BHs may
originate from SMSs at high redshifts.
Telescope Bibliographies: an Essential Component of Archival Data Management and Operations. (arXiv:1206.6352v1 [astro-ph.IM])
Telescope Bibliographies: an Essential Component of Archival Data Management and Operations. (arXiv:1206.6352v1 [astro-ph.IM]):
Assessing the impact of astronomical facilities rests upon an evaluation of
the scientific discoveries which their data have enabled. Telescope
bibliographies, which link data products with the literature, provide a way to
use bibliometrics as an impact measure for the underlying data. In this paper
we argue that the creation and maintenance of telescope bibliographies should
be considered an integral part of an observatory's operations. We review the
existing tools, services, and workflows which support these curation
activities, giving an estimate of the effort and expertise required to maintain
an archive-based telescope bibliography.
Assessing the impact of astronomical facilities rests upon an evaluation of
the scientific discoveries which their data have enabled. Telescope
bibliographies, which link data products with the literature, provide a way to
use bibliometrics as an impact measure for the underlying data. In this paper
we argue that the creation and maintenance of telescope bibliographies should
be considered an integral part of an observatory's operations. We review the
existing tools, services, and workflows which support these curation
activities, giving an estimate of the effort and expertise required to maintain
an archive-based telescope bibliography.
Molecular chemistry and the missing mass problem in PNe. (arXiv:1206.6301v1 [astro-ph.GA])
Molecular chemistry and the missing mass problem in PNe. (arXiv:1206.6301v1 [astro-ph.GA]):
Detections of molecular lines, mainly from H2$ and CO, reveal molecular
material in planetary nebulae. Observations of a variety of molecules suggest
that the molecular composition in these objects differs from that found in
interstellar clouds or in circumstellar envelopes. The success of the models,
which are mostly devoted to explain molecular densities in specific planetary
nebulae, is still partial, however. The present study aims at identifying the
influence of stellar and nebular properties on the molecular composition of
planetary nebulae by means of chemical models. A comparison of theoretical
results with those derived from the observations may provide clues to the
conditions that favor the presence of a particular molecule. A self-consistent
photoionization numerical code was adapted to simulate cold molecular regions
beyond the ionized zone. The code was used to obtain a grid of models and the
resulting column densities are compared with those inferred from observations.
Our models show that the inclusion of an incident flux of X-rays is required to
explain the molecular composition derived for planetary nebulae. We also obtain
a more accurate relation for the N(CO)/N(H2) ratio in these objects. Molecular
masses obtained by previous works in the literature were then recalculated,
showing that these masses can be underestimated by up to three orders of
magnitude. We conclude that the problem of the missing mass in planetary
nebulae can be solved by a more accurate calculation of the molecular mass.
Detections of molecular lines, mainly from H2$ and CO, reveal molecular
material in planetary nebulae. Observations of a variety of molecules suggest
that the molecular composition in these objects differs from that found in
interstellar clouds or in circumstellar envelopes. The success of the models,
which are mostly devoted to explain molecular densities in specific planetary
nebulae, is still partial, however. The present study aims at identifying the
influence of stellar and nebular properties on the molecular composition of
planetary nebulae by means of chemical models. A comparison of theoretical
results with those derived from the observations may provide clues to the
conditions that favor the presence of a particular molecule. A self-consistent
photoionization numerical code was adapted to simulate cold molecular regions
beyond the ionized zone. The code was used to obtain a grid of models and the
resulting column densities are compared with those inferred from observations.
Our models show that the inclusion of an incident flux of X-rays is required to
explain the molecular composition derived for planetary nebulae. We also obtain
a more accurate relation for the N(CO)/N(H2) ratio in these objects. Molecular
masses obtained by previous works in the literature were then recalculated,
showing that these masses can be underestimated by up to three orders of
magnitude. We conclude that the problem of the missing mass in planetary
nebulae can be solved by a more accurate calculation of the molecular mass.
An upper limit to the velocity dispersion of relaxed stellar systems without massive black holes. (arXiv:1206.6167v1 [astro-ph.GA])
An upper limit to the velocity dispersion of relaxed stellar systems without massive black holes. (arXiv:1206.6167v1 [astro-ph.GA]):
Massive black holes have been discovered in all closely examined galaxies
with high velocity dispersion. The case is not as clear for lower-dispersion
systems such as low-mass galaxies and globular clusters. Here we suggest that
above a critical velocity dispersion of roughly 40 km/s, massive central black
holes will form in relaxed stellar systems at any cosmic epoch. This is because
above this dispersion primordial binaries cannot support the system against
deep core collapse. If, as previous simulations show, the black holes formed in
the cluster settle to produce a dense subcluster, then given the extremely high
densities reached during core collapse the holes will merge with each other.
For low velocity dispersions and hence low cluster escape speeds, mergers will
typically kick out all or all but one of the holes due to three-body kicks or
the asymmetric emission of gravitational radiation. If one hole remains, it
will tidally disrupt stars at a high rate. If none remain, one is formed after
runaway collisions between stars, then it tidally disrupts stars at a high
rate. The accretion rate after disruption is many orders of magnitude above
Eddington. If, as several studies suggest, the hole can accept matter at that
rate because the generated radiation is trapped and advected, then it will grow
quickly and form a massive central black hole.
Massive black holes have been discovered in all closely examined galaxies
with high velocity dispersion. The case is not as clear for lower-dispersion
systems such as low-mass galaxies and globular clusters. Here we suggest that
above a critical velocity dispersion of roughly 40 km/s, massive central black
holes will form in relaxed stellar systems at any cosmic epoch. This is because
above this dispersion primordial binaries cannot support the system against
deep core collapse. If, as previous simulations show, the black holes formed in
the cluster settle to produce a dense subcluster, then given the extremely high
densities reached during core collapse the holes will merge with each other.
For low velocity dispersions and hence low cluster escape speeds, mergers will
typically kick out all or all but one of the holes due to three-body kicks or
the asymmetric emission of gravitational radiation. If one hole remains, it
will tidally disrupt stars at a high rate. If none remain, one is formed after
runaway collisions between stars, then it tidally disrupts stars at a high
rate. The accretion rate after disruption is many orders of magnitude above
Eddington. If, as several studies suggest, the hole can accept matter at that
rate because the generated radiation is trapped and advected, then it will grow
quickly and form a massive central black hole.
Simulating the Toothbrush: Evidence for a triple merger of galaxy clusters. (arXiv:1206.6118v2 [astro-ph.CO] UPDATED)
Simulating the Toothbrush: Evidence for a triple merger of galaxy clusters. (arXiv:1206.6118v2 [astro-ph.CO] UPDATED):
The newly discovered galaxy cluster 1RXS J0603.3+4214 hosts a 1.9 Mpc long,
bright radio relic with a peculiar linear morphology. Using hydrodynamical
+N-body AMR simulations of the merger between three initially hydrostatic
clusters in an idealised setup, we are able to reconstruct the morphology of
the radio relic. Based on our simulation, we can constrain the merger geometry,
predict lensing mass measurements and X-ray observations. Comparing such models
to X-ray, redshift and lensing data will validate the geometry of this complex
merger which helps to constrain the parameters for shock acceleration of
electrons that produces the radio relic.
The newly discovered galaxy cluster 1RXS J0603.3+4214 hosts a 1.9 Mpc long,
bright radio relic with a peculiar linear morphology. Using hydrodynamical
+N-body AMR simulations of the merger between three initially hydrostatic
clusters in an idealised setup, we are able to reconstruct the morphology of
the radio relic. Based on our simulation, we can constrain the merger geometry,
predict lensing mass measurements and X-ray observations. Comparing such models
to X-ray, redshift and lensing data will validate the geometry of this complex
merger which helps to constrain the parameters for shock acceleration of
electrons that produces the radio relic.
Origin of the anti-hierarchical growth of black holes. (arXiv:1206.6112v1 [astro-ph.CO])
Origin of the anti-hierarchical growth of black holes. (arXiv:1206.6112v1 [astro-ph.CO]):
Observational studies have revealed a "downsizing" trend in black hole (BH)
growth: the number densities of luminous AGN peak at higher redshifts than
those of faint AGN. This would seem to imply that massive black holes formed
before low mass black holes, in apparent contradiction to hierarchical
clustering scenarios. We investigate whether this observed "downsizing" in BH
growth is reproduced in a semi-analytic model for the formation and evolution
of galaxies and black holes, set within the hierarchical paradigm for structure
formation (Somerville et al. 2008; S08). In this model, black holes evolve from
light seeds (\sim100M\odot) and their growth is merger-driven. The original S08
model (baseline model) reproduces the number density of AGN at intermediate
redshifts and luminosities, but underproduces luminous AGN at very high
redshift (z > 3) and overproduces them at low redshift (z < 1). In addition,
the baseline model underproduces low-luminosity AGN at low redshift (z < 1). To
solve these problems we consider several modifications to the physical
processes in the model: (1) a 'heavy' black hole seeding scenario (2) a
sub-Eddington accretion rate ceiling that depends on the cold gas fraction, and
(3) an additional black hole accretion mode due to disk instabilities. With
these three modifications, the models can explain the observed downsizing,
successfully reproduce the bolometric AGN luminosity function and
simultaneously reproduce galaxy and black hole properties in the local
Universe. We also perform a comparison with the observed soft and hard X-ray
luminosity functions of AGN, including an empirical correction for torus-level
obscuration, and reach similar conclusions. Our best-fit model suggests a
scenario in which disk instabilities are the main driver for moderately
luminous Seyfert galaxies at low redshift, while major mergers are the main
trigger for luminous AGN.
Observational studies have revealed a "downsizing" trend in black hole (BH)
growth: the number densities of luminous AGN peak at higher redshifts than
those of faint AGN. This would seem to imply that massive black holes formed
before low mass black holes, in apparent contradiction to hierarchical
clustering scenarios. We investigate whether this observed "downsizing" in BH
growth is reproduced in a semi-analytic model for the formation and evolution
of galaxies and black holes, set within the hierarchical paradigm for structure
formation (Somerville et al. 2008; S08). In this model, black holes evolve from
light seeds (\sim100M\odot) and their growth is merger-driven. The original S08
model (baseline model) reproduces the number density of AGN at intermediate
redshifts and luminosities, but underproduces luminous AGN at very high
redshift (z > 3) and overproduces them at low redshift (z < 1). In addition,
the baseline model underproduces low-luminosity AGN at low redshift (z < 1). To
solve these problems we consider several modifications to the physical
processes in the model: (1) a 'heavy' black hole seeding scenario (2) a
sub-Eddington accretion rate ceiling that depends on the cold gas fraction, and
(3) an additional black hole accretion mode due to disk instabilities. With
these three modifications, the models can explain the observed downsizing,
successfully reproduce the bolometric AGN luminosity function and
simultaneously reproduce galaxy and black hole properties in the local
Universe. We also perform a comparison with the observed soft and hard X-ray
luminosity functions of AGN, including an empirical correction for torus-level
obscuration, and reach similar conclusions. Our best-fit model suggests a
scenario in which disk instabilities are the main driver for moderately
luminous Seyfert galaxies at low redshift, while major mergers are the main
trigger for luminous AGN.
Discovery of radio halos and double-relics in distant MACS galaxy clusters: clues to the efficiency of particle acceleration. (arXiv:1206.6102v1 [astro-ph.CO])
Discovery of radio halos and double-relics in distant MACS galaxy clusters: clues to the efficiency of particle acceleration. (arXiv:1206.6102v1 [astro-ph.CO]):
We have performed 323 MHz observations with the Giant Metrewave Radio
Telescope of the most promising candidates selected from the MACS catalog. The
aim of the work is to extend our knowledge of the radio halo and relic
populations to z>0.3, the epoch in which massive clusters formed. In
MACSJ1149.5+2223 and MACSJ1752.1+4440, we discovered two double-relic systems
with a radio halo, and in MACSJ0553.4-3342 we found a radio halo. Archival Very
Large Array observations and Westerbork Synthesis Radio Telescope observations
have been used to study the polarization and spectral index properties. The
radio halo in MACSJ1149.5+2223 has the steepest spectrum ever found so far in
these objects (alpha > 2). The double relics in MACSJ1149.5+2223 are peculiar
in their position that is misaligned with the main merger axis. The relics are
polarized up to 30% and 40% in MACSJ1149.5+2223 and MACSJ1752.040+44,
respectively. In both cases, the magnetic field is roughly aligned with the
relics' main axes. The spectra in the relics in MACSJ1752.040+44 steepen
towards the cluster centre, in agreement with model expectations. X-ray data on
MACSJ0553.4-3342 suggests that this cluster is undergoing a major merger, with
the merger axis close to the plane of the sky. The cores of the disrupted
clusters have just passed each other, but no radio relic is detected in this
system. If turbulence is responsible for the radio emission, we argue that it
must develop before the core passage. A comparison of double relic plus halo
system with cosmological simulations allows a simultaneous estimate of the
acceleration efficiencies at shocks (to produce relics) and of turbulence (to
produce the halo).
We have performed 323 MHz observations with the Giant Metrewave Radio
Telescope of the most promising candidates selected from the MACS catalog. The
aim of the work is to extend our knowledge of the radio halo and relic
populations to z>0.3, the epoch in which massive clusters formed. In
MACSJ1149.5+2223 and MACSJ1752.1+4440, we discovered two double-relic systems
with a radio halo, and in MACSJ0553.4-3342 we found a radio halo. Archival Very
Large Array observations and Westerbork Synthesis Radio Telescope observations
have been used to study the polarization and spectral index properties. The
radio halo in MACSJ1149.5+2223 has the steepest spectrum ever found so far in
these objects (alpha > 2). The double relics in MACSJ1149.5+2223 are peculiar
in their position that is misaligned with the main merger axis. The relics are
polarized up to 30% and 40% in MACSJ1149.5+2223 and MACSJ1752.040+44,
respectively. In both cases, the magnetic field is roughly aligned with the
relics' main axes. The spectra in the relics in MACSJ1752.040+44 steepen
towards the cluster centre, in agreement with model expectations. X-ray data on
MACSJ0553.4-3342 suggests that this cluster is undergoing a major merger, with
the merger axis close to the plane of the sky. The cores of the disrupted
clusters have just passed each other, but no radio relic is detected in this
system. If turbulence is responsible for the radio emission, we argue that it
must develop before the core passage. A comparison of double relic plus halo
system with cosmological simulations allows a simultaneous estimate of the
acceleration efficiencies at shocks (to produce relics) and of turbulence (to
produce the halo).
On the Importance of the Equation of State for the Neutrino-Driven Supernova Explosion Mechanism. (arXiv:1206.6101v1 [astro-ph.HE])
On the Importance of the Equation of State for the Neutrino-Driven Supernova Explosion Mechanism. (arXiv:1206.6101v1 [astro-ph.HE]):
We present results from spherically symmetric (1D) and axially symmetric (2D)
core-collapse supernova simulations. Our model is based on neutrino radiation
hydrodynamics, including spectral neutrino transport. We apply the equations of
state (EOS) from Lattimer & Swesty (LS) and Shen et al. (SHEN), and explore the
differences obtained during the post-bounce phase prior to the possible onset
of a neutrino-driven explosion. We confirm that in 1D simulations
neutrino-driven explosions cannot be obtained for any of the employed EOS. In
2D, EOS induced structural differences lead to a more efficient neutrino
heating, in particular for LS in comparison to the simulations that use SHEN.
For simulations of the 15 M_sun progenitor with LS under investigation, it
results in a continuous expansion of the stalled bounce shock to increasingly
larger radii, which is absent using SHEN. Simulations of a 11.2 M_sun
progenitor result in neutrino-driven explosions for all EOS under
investigation, however slightly more powerful for LS than for SHEN and also
slightly delayed for the latter. The generally more efficient neutrino heating
using LS can be related to the higher electron antineutrino luminosity and the
more mass enclosed inside the gain region. It also leads to the development of
an aspherical downflow of material from large radii to the central protoneutron
star surface for LS, which in turn supplies continuously energy to the
protoneutron star. Moreover, we investigate several additional indicators of
the explosion, e.g., the amplitude of the standing-accretion shock instability
mode, the mass weighted average entropy in the gain region, the protoneutron
star radius, the antesonic condition, and the ratio of advection and heating
timescales.
We present results from spherically symmetric (1D) and axially symmetric (2D)
core-collapse supernova simulations. Our model is based on neutrino radiation
hydrodynamics, including spectral neutrino transport. We apply the equations of
state (EOS) from Lattimer & Swesty (LS) and Shen et al. (SHEN), and explore the
differences obtained during the post-bounce phase prior to the possible onset
of a neutrino-driven explosion. We confirm that in 1D simulations
neutrino-driven explosions cannot be obtained for any of the employed EOS. In
2D, EOS induced structural differences lead to a more efficient neutrino
heating, in particular for LS in comparison to the simulations that use SHEN.
For simulations of the 15 M_sun progenitor with LS under investigation, it
results in a continuous expansion of the stalled bounce shock to increasingly
larger radii, which is absent using SHEN. Simulations of a 11.2 M_sun
progenitor result in neutrino-driven explosions for all EOS under
investigation, however slightly more powerful for LS than for SHEN and also
slightly delayed for the latter. The generally more efficient neutrino heating
using LS can be related to the higher electron antineutrino luminosity and the
more mass enclosed inside the gain region. It also leads to the development of
an aspherical downflow of material from large radii to the central protoneutron
star surface for LS, which in turn supplies continuously energy to the
protoneutron star. Moreover, we investigate several additional indicators of
the explosion, e.g., the amplitude of the standing-accretion shock instability
mode, the mass weighted average entropy in the gain region, the protoneutron
star radius, the antesonic condition, and the ratio of advection and heating
timescales.
Self-similarity of temperature profiles in distant galaxy clusters: the quest for a Universal law. (arXiv:1206.6603v1 [astro-ph.CO])
Self-similarity of temperature profiles in distant galaxy clusters: the quest for a Universal law. (arXiv:1206.6603v1 [astro-ph.CO]):
We present the XMM-Newton temperature profiles of 12 bright clusters of
galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles
(normalized by the mean temperature T500) are found to be generally
self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core
(NCC) clusters, by introducing a pseudo-entropy ratio
sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6
as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC
and NCC clusters differ mainly in the central regions, with the latters
exhibiting a marginally flatter central profile. A significant dependence of
the temperature profiles on the pseudo-entropy ratio sigma is detected by
fitting a function of both r and sigma, showing an indication that the outer
part of the profiles becomes steeper for higher values of sigma (i.e.
transitioning towards the NCC clusters). No significant evidence of redshift
evolution could be found within the redshift range sampled by our clusters
(0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at
0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have
experienced some sort of evolution. This can be due by the fact that higher z
clusters are at less advanced stage of their formation and did not have enough
time to create a relaxed structure, characterized by a central temperature dip
in CC clusters and by flatter profiles in NCC clusters. This is the first time
that a systematic study of the temperature profiles of galaxy clusters at z>0.4
has been attempted, as we were able to define the closest possible relation to
a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9,
showing a dependence on both the state of relaxation of the clusters and the
redshift.
We present the XMM-Newton temperature profiles of 12 bright clusters of
galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles
(normalized by the mean temperature T500) are found to be generally
self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core
(NCC) clusters, by introducing a pseudo-entropy ratio
sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6
as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC
and NCC clusters differ mainly in the central regions, with the latters
exhibiting a marginally flatter central profile. A significant dependence of
the temperature profiles on the pseudo-entropy ratio sigma is detected by
fitting a function of both r and sigma, showing an indication that the outer
part of the profiles becomes steeper for higher values of sigma (i.e.
transitioning towards the NCC clusters). No significant evidence of redshift
evolution could be found within the redshift range sampled by our clusters
(0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at
0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have
experienced some sort of evolution. This can be due by the fact that higher z
clusters are at less advanced stage of their formation and did not have enough
time to create a relaxed structure, characterized by a central temperature dip
in CC clusters and by flatter profiles in NCC clusters. This is the first time
that a systematic study of the temperature profiles of galaxy clusters at z>0.4
has been attempted, as we were able to define the closest possible relation to
a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9,
showing a dependence on both the state of relaxation of the clusters and the
redshift.
Mixing of Clumpy Supernova Ejecta into Molecular Clouds. (arXiv:1206.6516v1 [astro-ph.SR])
Mixing of Clumpy Supernova Ejecta into Molecular Clouds. (arXiv:1206.6516v1 [astro-ph.SR]):
Several lines of evidence, from isotopic analyses of meteorites to studies of
the Sun's elemental and isotopic composition, indicate that the solar system
was contaminated early in its evolution by ejecta from a nearby supernova (SN).
Previous models have invoked SN material being injected into an extant
protoplanetary disk, or isotropically expanding ejecta sweeping over a distant
(>10 pc) cloud core, simultaneously enriching it and triggering its collapse.
Here we consider a new astrophysical setting: the injection of clumpy SN
ejecta, as observed in the Cas A SN remnant, into the molecular gas at the
periphery of an HII region created by the SN's progenitor star. To track these
interactions we have conducted a suite of high-resolution (1500^3 effective) 3D
simulations that follow the evolution of individual clumps as they move into
molecular gas. Even at these high resolutions, our simulations do not quite
achieve numerical convergence, due to the challenge of properly resolving the
small-scale mixing of ejecta and molecular gas, although they do allow some
robust conclusions to be drawn. Isotropically exploding ejecta do not penetrate
into the molecular cloud, but, if cooling is properly accounted for, clumpy
ejecta penetrate to distances ~10^18 cm and mix effectively with star-forming
molecular gas. The ~2 M_\odot high-metallicity ejecta from a core-collapse SN
is likely to mix with ~2 \times 10^4 M_\odot of molecular gas. Thus all stars
forming late (~5 Myr) in the evolution of an HII region may be contaminated by
SN ejecta at a level ~10^-4. This level of contamination is consistent with the
abundances of short-lived radionuclides and possibly some stable isotopic
shifts in the early solar system, and is potentially consistent with the
observed variability in stellar elemental abundances. SN contamination of
forming planetary systems may be a common, universal process.
Several lines of evidence, from isotopic analyses of meteorites to studies of
the Sun's elemental and isotopic composition, indicate that the solar system
was contaminated early in its evolution by ejecta from a nearby supernova (SN).
Previous models have invoked SN material being injected into an extant
protoplanetary disk, or isotropically expanding ejecta sweeping over a distant
(>10 pc) cloud core, simultaneously enriching it and triggering its collapse.
Here we consider a new astrophysical setting: the injection of clumpy SN
ejecta, as observed in the Cas A SN remnant, into the molecular gas at the
periphery of an HII region created by the SN's progenitor star. To track these
interactions we have conducted a suite of high-resolution (1500^3 effective) 3D
simulations that follow the evolution of individual clumps as they move into
molecular gas. Even at these high resolutions, our simulations do not quite
achieve numerical convergence, due to the challenge of properly resolving the
small-scale mixing of ejecta and molecular gas, although they do allow some
robust conclusions to be drawn. Isotropically exploding ejecta do not penetrate
into the molecular cloud, but, if cooling is properly accounted for, clumpy
ejecta penetrate to distances ~10^18 cm and mix effectively with star-forming
molecular gas. The ~2 M_\odot high-metallicity ejecta from a core-collapse SN
is likely to mix with ~2 \times 10^4 M_\odot of molecular gas. Thus all stars
forming late (~5 Myr) in the evolution of an HII region may be contaminated by
SN ejecta at a level ~10^-4. This level of contamination is consistent with the
abundances of short-lived radionuclides and possibly some stable isotopic
shifts in the early solar system, and is potentially consistent with the
observed variability in stellar elemental abundances. SN contamination of
forming planetary systems may be a common, universal process.
Radio AGN in galaxy clusters: heating hot atmospheres and driving supermassive black hole growth over cosmic time. (arXiv:1206.7071v1 [astro-ph.CO])
Radio AGN in galaxy clusters: heating hot atmospheres and driving supermassive black hole growth over cosmic time. (arXiv:1206.7071v1 [astro-ph.CO]):
We estimate the average radio-AGN (mechanical) power deposited into the hot
atmospheres of galaxy clusters over more than three quarters of the age of the
Universe. Our sample was drawn from eight major X-ray cluster surveys, and
includes 685 clusters in the redshift range 0.1<z<0.6 that overlap the area
covered by the NVSS. The radio-AGN mechanical power was estimated by scaling
the radio luminosity of central NVSS radio sources using the relation between
the radio synchrotron luminosities and X-ray cavity power measurements of
Cavagnolo et al. (2010). We find only a weak correlation between radio
luminosity and cluster X-ray luminosity across the sample. This trend is driven
primarily by the most distant clusters, where the detection fraction and
average radio powers are higher in the most luminous X-ray clusters at
redshifts at or above z=0.3. The average AGN mechanical power of
$3\times10^{44}$ erg/s exceeds the X-ray luminosity of 44% of the clusters in
our sample, indicating that the accumulation of radio-AGN energy is significant
in these clusters. Integrating the AGN mechanical power to redshift z = 2.0,
using simple models for its evolution and disregarding the hierarchical growth
of clusters, we find that the AGN energy accumulated per particle in low
luminosity X-ray clusters exceeds 1.0 keV per particle. This conservative
estimate is comparable to the level of energy needed to "preheat" clusters,
indicating that continual outbursts from radio-AGN are a significant source of
gas energy in hot atmospheres. Our result implies that the supermassive black
holes in brightest cluster galaxies that generated this energy did so by
accreting an average of 10^9 M_sun over time, which is comparable to the rapid
level of growth expected during the quasar era.
We estimate the average radio-AGN (mechanical) power deposited into the hot
atmospheres of galaxy clusters over more than three quarters of the age of the
Universe. Our sample was drawn from eight major X-ray cluster surveys, and
includes 685 clusters in the redshift range 0.1<z<0.6 that overlap the area
covered by the NVSS. The radio-AGN mechanical power was estimated by scaling
the radio luminosity of central NVSS radio sources using the relation between
the radio synchrotron luminosities and X-ray cavity power measurements of
Cavagnolo et al. (2010). We find only a weak correlation between radio
luminosity and cluster X-ray luminosity across the sample. This trend is driven
primarily by the most distant clusters, where the detection fraction and
average radio powers are higher in the most luminous X-ray clusters at
redshifts at or above z=0.3. The average AGN mechanical power of
$3\times10^{44}$ erg/s exceeds the X-ray luminosity of 44% of the clusters in
our sample, indicating that the accumulation of radio-AGN energy is significant
in these clusters. Integrating the AGN mechanical power to redshift z = 2.0,
using simple models for its evolution and disregarding the hierarchical growth
of clusters, we find that the AGN energy accumulated per particle in low
luminosity X-ray clusters exceeds 1.0 keV per particle. This conservative
estimate is comparable to the level of energy needed to "preheat" clusters,
indicating that continual outbursts from radio-AGN are a significant source of
gas energy in hot atmospheres. Our result implies that the supermassive black
holes in brightest cluster galaxies that generated this energy did so by
accreting an average of 10^9 M_sun over time, which is comparable to the rapid
level of growth expected during the quasar era.
Ram pressure stripping in elliptical galaxies: I. the impact of the interstellar medium turbulence. (arXiv:1206.6947v2 [astro-ph.CO] UPDATED)
Ram pressure stripping in elliptical galaxies: I. the impact of the interstellar medium turbulence. (arXiv:1206.6947v2 [astro-ph.CO] UPDATED):
Elliptical galaxies contain X-ray emitting gas that is subject to continuous
ram pressure stripping over timescales comparable to cluster ages. The gas in
these galaxies is not in perfect hydrostatic equilibrium. Supernova feedback,
stellar winds, or active galactic nuclei (AGN) feedback can significantly
perturb the interstellar medium (ISM). Using hydrodynamical simulations, we
investigate the effect of subsonic turbulence in the hot ISM on the ram
pressure stripping process in early-type galaxies. We find that galaxies with
more turbulent ISM produce longer, wider, and more smoothly distributed tails
of the stripped ISM than those characterised by weaker ISM turbulence. Our main
conclusion is that even very weak internal turbulence, at the level of <15% of
the average ISM sound speed, can significantly accelerate the gas removal from
galaxies via ram pressure stripping. The magnitude of this effect increases
sharply with the strength of turbulence. As most of the gas stripping takes
place near the boundary between the ISM and the intraclustermedium (ICM), the
boost in the ISM stripping rate is due to the "random walk" of the ISM from the
central regions of the galactic potential well to larger distances, where the
ram pressure is able to permanently remove the gas from galaxies. The ICM can
be temporarily trapped inside the galactic potential well due to the mixing of
the turbulent ISM with the ICM. The galaxies with more turbulent ISM, yet still
characterised by very weak turbulence, can hold larger amounts of the ICM.
[Abridged]
Elliptical galaxies contain X-ray emitting gas that is subject to continuous
ram pressure stripping over timescales comparable to cluster ages. The gas in
these galaxies is not in perfect hydrostatic equilibrium. Supernova feedback,
stellar winds, or active galactic nuclei (AGN) feedback can significantly
perturb the interstellar medium (ISM). Using hydrodynamical simulations, we
investigate the effect of subsonic turbulence in the hot ISM on the ram
pressure stripping process in early-type galaxies. We find that galaxies with
more turbulent ISM produce longer, wider, and more smoothly distributed tails
of the stripped ISM than those characterised by weaker ISM turbulence. Our main
conclusion is that even very weak internal turbulence, at the level of <15% of
the average ISM sound speed, can significantly accelerate the gas removal from
galaxies via ram pressure stripping. The magnitude of this effect increases
sharply with the strength of turbulence. As most of the gas stripping takes
place near the boundary between the ISM and the intraclustermedium (ICM), the
boost in the ISM stripping rate is due to the "random walk" of the ISM from the
central regions of the galactic potential well to larger distances, where the
ram pressure is able to permanently remove the gas from galaxies. The ICM can
be temporarily trapped inside the galactic potential well due to the mixing of
the turbulent ISM with the ICM. The galaxies with more turbulent ISM, yet still
characterised by very weak turbulence, can hold larger amounts of the ICM.
[Abridged]
Superfluidity and entrainment in neutron-star crusts. (arXiv:1206.6926v1 [astro-ph.HE])
Superfluidity and entrainment in neutron-star crusts. (arXiv:1206.6926v1 [astro-ph.HE]):
Despite the absence of viscous drag, the neutron superfluid permeating the
inner crust of a neutron star can still be strongly coupled to nuclei due to
non-dissipative entrainment effects. Neutron superfluidity and entrainment have
been systematically studied in all regions of the inner crust of a cold
non-accreting neutron star in the framework of the band theory of solids. It is
shown that in the intermediate layers of the inner crust a large fraction of
"free" neutrons are actually entrained by the crust. The results suggest that a
revision of the interpretation of many observable astrophysical phenomena might
be necessary.
Despite the absence of viscous drag, the neutron superfluid permeating the
inner crust of a neutron star can still be strongly coupled to nuclei due to
non-dissipative entrainment effects. Neutron superfluidity and entrainment have
been systematically studied in all regions of the inner crust of a cold
non-accreting neutron star in the framework of the band theory of solids. It is
shown that in the intermediate layers of the inner crust a large fraction of
"free" neutrons are actually entrained by the crust. The results suggest that a
revision of the interpretation of many observable astrophysical phenomena might
be necessary.
Structure of neutron stars with unified equations of state. (arXiv:1206.6922v1 [astro-ph.HE])
Structure of neutron stars with unified equations of state. (arXiv:1206.6922v1 [astro-ph.HE]):
We present a set of three unified equations of states (EoSs) based on the
nuclear energy-density functional (EDF) theory.These EoSs are based on
generalized Skyrme forces fitted to essentially all experimental atomic mass
data and constrained to reproduce various properties of infinite nuclear matter
as obtained from many-body calculations using realistic two- and three-body
interactions. The structure of cold isolated neutron stars is discussed in
connection with some astrophysical observations.
We present a set of three unified equations of states (EoSs) based on the
nuclear energy-density functional (EDF) theory.These EoSs are based on
generalized Skyrme forces fitted to essentially all experimental atomic mass
data and constrained to reproduce various properties of infinite nuclear matter
as obtained from many-body calculations using realistic two- and three-body
interactions. The structure of cold isolated neutron stars is discussed in
connection with some astrophysical observations.
The Chandra X-ray point source catalog in the DEEP2 Galaxy Redshift Survey fields. (arXiv:1206.6884v1 [astro-ph.HE])
The Chandra X-ray point source catalog in the DEEP2 Galaxy Redshift Survey fields. (arXiv:1206.6884v1 [astro-ph.HE]):
We present the X-ray point-source catalog produced from the Chandra Advanced
CCD Imaging Spectrometer (ACIS-I) observations of the combined \sim3.2 deg2
DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1 deg2 fields. The
combined total exposures across all four XDEEP2 fields range from ~10ks-1.1Ms.
We detect X-ray point-sources in both the individual ACIS-I observations and
the overlapping regions in the merged (stacked) images. We find a total of 2976
unique X-ray sources within the survey area with an expected false-source
contamination of ~30 sources (~1%). We present the combined logN-logS
distribution of sources detected across the XDEEP2 survey fields and find good
agreement with the Extended Chandra Deep Field and Chandra-COSMOS fields to
f_{X,0.5-2keV}\sim2x10^{-16} erg/cm^2/s. Given the large survey area of XDEEP2,
we additionally place relatively strong constraints on the logN-logS
distribution at high fluxes (f_{X,0.5-2keV}\sim3x10^{-14} erg/cm^2/s), and find
a small systematic offset (a factor ~1.5) towards lower source numbers in this
regime, when compared to smaller area surveys. The number counts observed in
XDEEP2 are in close agreement with those predicted by X-ray background
synthesis models. Additionally, we present a Bayesian-style method for
associating the X-ray sources with optical photometric counterparts in the
DEEP2 catalog (complete to R_AB < 25.2) and find that 2126 (~71.4\pm2.8%) of
the 2976 X-ray sources presented here have a secure optical counterpart with a
<6% contamination fraction. We provide the DEEP2 optical source properties
(e.g., magnitude, redshift) as part of the X-ray-optical counterpart catalog.
We present the X-ray point-source catalog produced from the Chandra Advanced
CCD Imaging Spectrometer (ACIS-I) observations of the combined \sim3.2 deg2
DEEP2 (XDEEP2) survey fields, which consist of four ~0.7-1.1 deg2 fields. The
combined total exposures across all four XDEEP2 fields range from ~10ks-1.1Ms.
We detect X-ray point-sources in both the individual ACIS-I observations and
the overlapping regions in the merged (stacked) images. We find a total of 2976
unique X-ray sources within the survey area with an expected false-source
contamination of ~30 sources (~1%). We present the combined logN-logS
distribution of sources detected across the XDEEP2 survey fields and find good
agreement with the Extended Chandra Deep Field and Chandra-COSMOS fields to
f_{X,0.5-2keV}\sim2x10^{-16} erg/cm^2/s. Given the large survey area of XDEEP2,
we additionally place relatively strong constraints on the logN-logS
distribution at high fluxes (f_{X,0.5-2keV}\sim3x10^{-14} erg/cm^2/s), and find
a small systematic offset (a factor ~1.5) towards lower source numbers in this
regime, when compared to smaller area surveys. The number counts observed in
XDEEP2 are in close agreement with those predicted by X-ray background
synthesis models. Additionally, we present a Bayesian-style method for
associating the X-ray sources with optical photometric counterparts in the
DEEP2 catalog (complete to R_AB < 25.2) and find that 2126 (~71.4\pm2.8%) of
the 2976 X-ray sources presented here have a secure optical counterpart with a
<6% contamination fraction. We provide the DEEP2 optical source properties
(e.g., magnitude, redshift) as part of the X-ray-optical counterpart catalog.
Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center. (arXiv:1206.6882v1 [astro-ph.HE])
Interacting Cosmic Rays with Molecular Clouds: A Bremsstrahlung Origin of Diffuse High Energy Emission from the Inner 2deg by 1deg of the Galactic Center. (arXiv:1206.6882v1 [astro-ph.HE]):
The high energy activity in the inner few degrees of the Galactic center is
traced by diffuse radio, X-ray and gamma-ray emission. The physical
relationship between different components of diffuse gas emitting at multiple
wavelengths is a focus of this work. We first present radio continuum
observations using Green Bank Telescope and model the nonthermal spectrum in
terms of a broken power-law distribution of GeV electrons emitting synchrotron
radiation. We show that the emission detected by Fermi is primarily due to
nonthermal bremsstrahlung produced by the population of synchrotron emitting
electrons in the GeV energy range interacting with neutral gas. The
extrapolation of the electron population measured from radio data to low and
high energies can also explain the origin of FeI 6.4 keV line and diffuse TeV
emission, as observed with Suzaku, XMM-Newton, Chandra and the H.E.S.S.
observatories. The inferred physical quantities from modeling multi-wavelength
emission in the context of bremsstrahlung emission from the inner 300x120
parsecs of the Galactic center are constrained to have the cosmic ray
ionization rate 1-10x10^{-15} s^-1, molecular gas heating rate elevating the
gas temperature to 75-200K, fractional ionization of molecular gas 10^{-6} to
10^{-5}, large scale magnetic field 10-20 micro Gauss, the density of diffuse
and dense molecular gas 100 and 10^3 cm^{-3} over 300pc and 50pc pathlengths,
and the variability of FeI Kalpha 6.4 keV line emission on yearly time scales.
Important implications of our study are that GeV electrons emitting in radio
can explain the GeV gamma-rays detected by Fermi and that the cosmic ray
irradiation model, like the model of the X-ray irradiation triggered by past
activity of Sgr A*, can also explain the origin of the variable 6.4 keV
emission from Galactic center molecular clouds.
The high energy activity in the inner few degrees of the Galactic center is
traced by diffuse radio, X-ray and gamma-ray emission. The physical
relationship between different components of diffuse gas emitting at multiple
wavelengths is a focus of this work. We first present radio continuum
observations using Green Bank Telescope and model the nonthermal spectrum in
terms of a broken power-law distribution of GeV electrons emitting synchrotron
radiation. We show that the emission detected by Fermi is primarily due to
nonthermal bremsstrahlung produced by the population of synchrotron emitting
electrons in the GeV energy range interacting with neutral gas. The
extrapolation of the electron population measured from radio data to low and
high energies can also explain the origin of FeI 6.4 keV line and diffuse TeV
emission, as observed with Suzaku, XMM-Newton, Chandra and the H.E.S.S.
observatories. The inferred physical quantities from modeling multi-wavelength
emission in the context of bremsstrahlung emission from the inner 300x120
parsecs of the Galactic center are constrained to have the cosmic ray
ionization rate 1-10x10^{-15} s^-1, molecular gas heating rate elevating the
gas temperature to 75-200K, fractional ionization of molecular gas 10^{-6} to
10^{-5}, large scale magnetic field 10-20 micro Gauss, the density of diffuse
and dense molecular gas 100 and 10^3 cm^{-3} over 300pc and 50pc pathlengths,
and the variability of FeI Kalpha 6.4 keV line emission on yearly time scales.
Important implications of our study are that GeV electrons emitting in radio
can explain the GeV gamma-rays detected by Fermi and that the cosmic ray
irradiation model, like the model of the X-ray irradiation triggered by past
activity of Sgr A*, can also explain the origin of the variable 6.4 keV
emission from Galactic center molecular clouds.
Observable Consequences of Merger-Driven Gaps and Holes in Black Hole Accretion Disks. (arXiv:1207.0296v1 [astro-ph.HE])
Observable Consequences of Merger-Driven Gaps and Holes in Black Hole Accretion Disks. (arXiv:1207.0296v1 [astro-ph.HE]):
We calculate the observable signature of a black hole accretion disk with a
gap or hole created by a secondary black hole embedded in the disk. We find
that for an interesting range of parameters of black hole masses (~10^6 to 10^9
Msun), orbital separation (~1 AU to ~1 pc), and gap width (10--180 disk scale
heights), the missing thermal emission from a gap manifests itself in an
observable decrement in the spectral energy distribution. We present
observational diagnostics in terms of powerlaw forms that can be fit to
line-free regions in AGN spectra or in fluxes from sequences of broad filters.
Most interestingly, the change in slope in the broken powerlaw is almost
entirely dependent on the width of gap in the accretion disk, which in turn is
uniquely determined by mass ratio of the black holes, such that it scales
roughly as $q^{5/4}$. Thus one can use spectral observations of the continuum
of bright active galactic nuclei to infer not only the presence of a closely
separated black hole binary but also the mass ratio. When the black hole merger
opens a hole in the inner disk, the broad band SED of the AGN or quasar may
serve as a diagnostic. Such sources should be especially luminous in optical
bands but intrinsically faint in X-rays (i.e., not merely obscured). We briefly
note that viable candidates may have already been identified.
We calculate the observable signature of a black hole accretion disk with a
gap or hole created by a secondary black hole embedded in the disk. We find
that for an interesting range of parameters of black hole masses (~10^6 to 10^9
Msun), orbital separation (~1 AU to ~1 pc), and gap width (10--180 disk scale
heights), the missing thermal emission from a gap manifests itself in an
observable decrement in the spectral energy distribution. We present
observational diagnostics in terms of powerlaw forms that can be fit to
line-free regions in AGN spectra or in fluxes from sequences of broad filters.
Most interestingly, the change in slope in the broken powerlaw is almost
entirely dependent on the width of gap in the accretion disk, which in turn is
uniquely determined by mass ratio of the black holes, such that it scales
roughly as $q^{5/4}$. Thus one can use spectral observations of the continuum
of bright active galactic nuclei to infer not only the presence of a closely
separated black hole binary but also the mass ratio. When the black hole merger
opens a hole in the inner disk, the broad band SED of the AGN or quasar may
serve as a diagnostic. Such sources should be especially luminous in optical
bands but intrinsically faint in X-rays (i.e., not merely obscured). We briefly
note that viable candidates may have already been identified.
Cosmological Constraints from a Combination of Galaxy Clustering & Lensing -- II. Fisher Matrix Analysis. (arXiv:1207.0004v1 [astro-ph.CO])
Cosmological Constraints from a Combination of Galaxy Clustering & Lensing -- II. Fisher Matrix Analysis. (arXiv:1207.0004v1 [astro-ph.CO]):
We quantify the accuracy with which the cosmological parameters
characterizing the energy density of matter (\Omega_m), the amplitude of the
power spectrum of matter fluctuations (\sigma_8), the energy density of
neutrinos (\Omega_{\nu}) and the dark energy equation of state (w_0) can be
constrained using data from large galaxy redshift surveys. We advocate a joint
analysis of the abundance of galaxies, galaxy clustering, and the galaxy-galaxy
weak lensing signal in order to simultaneously constrain the halo occupation
statistics (i.e., galaxy bias) and the cosmological parameters of interest. We
parameterize the halo occupation distribution of galaxies in terms of the
conditional luminosity function and use the analytical framework of the halo
model described in our companion paper (van den Bosch et al. 2012), to predict
the relevant observables. By performing a Fisher matrix analysis, we show that
a joint analysis of these observables, even with the precision with which they
are currently measured from the Sloan Digital Sky Survey, can be used to obtain
tight constraints on the cosmological parameters, fully marginalized over
uncertainties in galaxy bias. We demonstrate that the cosmological constraints
from such an analysis are nearly uncorrelated with the halo occupation
distribution constraints, thus, minimizing the systematic impact of any
imperfections in modeling the halo occupation statistics on the cosmological
constraints. In fact, we demonstrate that the constraints from such an analysis
are both complementary to and competitive with existing constraints on these
parameters from a number of other techniques, such as cluster abundances,
cosmic shear and/or baryon acoustic oscillations, thus paving the way to test
the concordance cosmological model.
We quantify the accuracy with which the cosmological parameters
characterizing the energy density of matter (\Omega_m), the amplitude of the
power spectrum of matter fluctuations (\sigma_8), the energy density of
neutrinos (\Omega_{\nu}) and the dark energy equation of state (w_0) can be
constrained using data from large galaxy redshift surveys. We advocate a joint
analysis of the abundance of galaxies, galaxy clustering, and the galaxy-galaxy
weak lensing signal in order to simultaneously constrain the halo occupation
statistics (i.e., galaxy bias) and the cosmological parameters of interest. We
parameterize the halo occupation distribution of galaxies in terms of the
conditional luminosity function and use the analytical framework of the halo
model described in our companion paper (van den Bosch et al. 2012), to predict
the relevant observables. By performing a Fisher matrix analysis, we show that
a joint analysis of these observables, even with the precision with which they
are currently measured from the Sloan Digital Sky Survey, can be used to obtain
tight constraints on the cosmological parameters, fully marginalized over
uncertainties in galaxy bias. We demonstrate that the cosmological constraints
from such an analysis are nearly uncorrelated with the halo occupation
distribution constraints, thus, minimizing the systematic impact of any
imperfections in modeling the halo occupation statistics on the cosmological
constraints. In fact, we demonstrate that the constraints from such an analysis
are both complementary to and competitive with existing constraints on these
parameters from a number of other techniques, such as cluster abundances,
cosmic shear and/or baryon acoustic oscillations, thus paving the way to test
the concordance cosmological model.
Re-examining the XMM-Newton Spectrum of the Black Hole Candidate XTE J1652-453. (arXiv:1207.0682v1 [astro-ph.HE])
Re-examining the XMM-Newton Spectrum of the Black Hole Candidate XTE J1652-453. (arXiv:1207.0682v1 [astro-ph.HE]):
The XMM-Newton spectrum of the black hole candidate XTE J1652-453 shows a
broad and strong Fe K-alpha emission line, generally believed to originate from
reflection of the inner accretion disc. These data have been analysed by
Hiemstra et al. (2011) using a variety of phenomenological models. We
re-examine the spectrum with a self-consistent relativistic reflection model. A
narrow absorption line near 7.2 keV may be present, which if real is likely the
Fe XXVI absorption line arising from highly ionised, rapidly outflowing disc
wind. The blue shift of this feature corresponds to a velocity of about 11100
km/s, which is much larger than the typical values seen in stellar-mass black
holes. Given that we also find the source to have a low inclination (i < 32
degrees; close to face-on), we would therefore be seeing through the very base
of outflow. This could be a possible explanation for the unusually high
velocity. We use a reflection model combined with a relativistic convolution
kernel which allows for both prograde and retrograde black hole spin, and treat
the potential absorption feature with a physical model for a photo-ionised
plasma. In this manner, assuming the disc is not truncated, we could only
constrain the spin of the black hole in XTE J1652-453 to be less than ~ 0.5
Jc/GM^{2} at the 90% confidence limit.
The XMM-Newton spectrum of the black hole candidate XTE J1652-453 shows a
broad and strong Fe K-alpha emission line, generally believed to originate from
reflection of the inner accretion disc. These data have been analysed by
Hiemstra et al. (2011) using a variety of phenomenological models. We
re-examine the spectrum with a self-consistent relativistic reflection model. A
narrow absorption line near 7.2 keV may be present, which if real is likely the
Fe XXVI absorption line arising from highly ionised, rapidly outflowing disc
wind. The blue shift of this feature corresponds to a velocity of about 11100
km/s, which is much larger than the typical values seen in stellar-mass black
holes. Given that we also find the source to have a low inclination (i < 32
degrees; close to face-on), we would therefore be seeing through the very base
of outflow. This could be a possible explanation for the unusually high
velocity. We use a reflection model combined with a relativistic convolution
kernel which allows for both prograde and retrograde black hole spin, and treat
the potential absorption feature with a physical model for a photo-ionised
plasma. In this manner, assuming the disc is not truncated, we could only
constrain the spin of the black hole in XTE J1652-453 to be less than ~ 0.5
Jc/GM^{2} at the 90% confidence limit.
Updated Atomic Data and Calculations for X-ray Spectroscopy. (arXiv:1207.0576v1 [astro-ph.HE])
Updated Atomic Data and Calculations for X-ray Spectroscopy. (arXiv:1207.0576v1 [astro-ph.HE]):
We describe the latest release of AtomDB, version 2.0.2, a database of atomic
data and a plasma modeling code with a focus on X-ray astronomy. This release
includes several major updates to the fundamental atomic structure and process
data held within AtomDB, incorporating new ionization balance data,
state-selective recombination data, and updated collisional excitation data for
many ions, including the iron L-shell ions from Fe$^{+16}$ to Fe$^{+23}$ and
all of the hydrogen- and helium-like sequences. We also describe some of the
effects that these changes have on calculated emission and diagnostic line
ratios, such as changes in the temperature implied by the He-like G-ratios of
up to a factor of 2.
We describe the latest release of AtomDB, version 2.0.2, a database of atomic
data and a plasma modeling code with a focus on X-ray astronomy. This release
includes several major updates to the fundamental atomic structure and process
data held within AtomDB, incorporating new ionization balance data,
state-selective recombination data, and updated collisional excitation data for
many ions, including the iron L-shell ions from Fe$^{+16}$ to Fe$^{+23}$ and
all of the hydrogen- and helium-like sequences. We also describe some of the
effects that these changes have on calculated emission and diagnostic line
ratios, such as changes in the temperature implied by the He-like G-ratios of
up to a factor of 2.
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- III. Application to SDSS Data. (arXiv:1207.0503v1 [astro-ph.CO])
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- III. Application to SDSS Data. (arXiv:1207.0503v1 [astro-ph.CO]):
We simultaneously constrain cosmology and galaxy bias using measurements of
galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the
Sloan Digital Sky Survey. We use the conditional luminosity function (which
describes the halo occupation statistics as function of galaxy luminosity)
combined with the halo model (which describes the non-linear matter field in
terms of its halo building blocks) to describe the galaxy-dark matter
connection. We explicitly account for residual redshift space distortions in
the projected galaxy-galaxy correlation functions, and marginalize over
uncertainties in the scale dependence of the halo bias and the detailed
structure of dark matter haloes. Under the assumption of a spatially flat,
vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density,
{\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and
we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the
baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8
= 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties
in the radial number density distribution of satellite galaxies, while allowing
for non-Poisson satellite occupation distributions results in a slightly lower
value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in
excellent agreement (at the 1{\sigma} level) with the cosmic microwave
background constraints from WMAP. This demonstrates that the use of a realistic
and accurate model for galaxy bias, down to the smallest non-linear scales
currently observed in galaxy surveys, leads to results perfectly consistent
with the vanilla {\Lambda}CDM cosmology.
We simultaneously constrain cosmology and galaxy bias using measurements of
galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the
Sloan Digital Sky Survey. We use the conditional luminosity function (which
describes the halo occupation statistics as function of galaxy luminosity)
combined with the halo model (which describes the non-linear matter field in
terms of its halo building blocks) to describe the galaxy-dark matter
connection. We explicitly account for residual redshift space distortions in
the projected galaxy-galaxy correlation functions, and marginalize over
uncertainties in the scale dependence of the halo bias and the detailed
structure of dark matter haloes. Under the assumption of a spatially flat,
vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density,
{\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and
we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the
baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8
= 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties
in the radial number density distribution of satellite galaxies, while allowing
for non-Poisson satellite occupation distributions results in a slightly lower
value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in
excellent agreement (at the 1{\sigma} level) with the cosmic microwave
background constraints from WMAP. This demonstrates that the use of a realistic
and accurate model for galaxy bias, down to the smallest non-linear scales
currently observed in galaxy surveys, leads to results perfectly consistent
with the vanilla {\Lambda}CDM cosmology.
Multiwavelength campaign on Mrk 509: Reverberation of the Fe Kalpha line. (arXiv:1207.0831v1 [astro-ph.HE])
Multiwavelength campaign on Mrk 509: Reverberation of the Fe Kalpha line. (arXiv:1207.0831v1 [astro-ph.HE]):
We report on a detailed study of the Fe K emission/absorption complex in the
nearby, bright Seyfert 1 galaxy Mrk 509. The study is part of an extensive
XMM-Newton monitoring consisting of 10 pointings (~60 ks each) about once every
four days, and includes also a reanalysis of previous XMM-Newton and Chandra
observations. Mrk 509 shows a clear (EW=58 eV) neutral Fe Kalpha emission line
that can be decomposed into a narrow (sigma=0.027 keV) component (found in the
Chandra HETG data) plus a resolved (sigma=0.22 keV) component. We find the
first successful measurement of a linear correlation between the intensity of
the resolved line component and the 3-10 keV flux variations on time-scales of
years down to a few days. The Fe Kalpha reverberates the hard X-ray continuum
without any measurable lag, suggesting that the region producing the resolved
Fe Kalpha component is located within a few light days-week (r<~10^3 rg) from
the Black Hole (BH). The lack of a redshifted wing in the line poses a lower
limit of >40 rg for its distance from the BH. The Fe Kalpha could thus be
emitted from the inner regions of the BLR, i.e. within the ~80 light days
indicated by the Hbeta line measurements. In addition to these two neutral Fe
Kalpha components, we confirm the detection of weak (EW~8-20 eV) ionised Fe K
emission. This ionised line can be modeled with either a blend of two narrow
FeXXV and FeXXVI emission lines or with a single relativistic line produced, in
an ionised disc, down to a few rg from the BH. Finally, we observe a
weakening/disappearing of the medium and high velocity high ionisation Fe K
wind features found in previous XMM-Newton observations. This campaign has made
possible the first reverberation measurement of the resolved component of the
Fe Kalpha line, from which we can infer a location for the bulk of its emission
at a distance of r~40-1000 rg from the BH.
We report on a detailed study of the Fe K emission/absorption complex in the
nearby, bright Seyfert 1 galaxy Mrk 509. The study is part of an extensive
XMM-Newton monitoring consisting of 10 pointings (~60 ks each) about once every
four days, and includes also a reanalysis of previous XMM-Newton and Chandra
observations. Mrk 509 shows a clear (EW=58 eV) neutral Fe Kalpha emission line
that can be decomposed into a narrow (sigma=0.027 keV) component (found in the
Chandra HETG data) plus a resolved (sigma=0.22 keV) component. We find the
first successful measurement of a linear correlation between the intensity of
the resolved line component and the 3-10 keV flux variations on time-scales of
years down to a few days. The Fe Kalpha reverberates the hard X-ray continuum
without any measurable lag, suggesting that the region producing the resolved
Fe Kalpha component is located within a few light days-week (r<~10^3 rg) from
the Black Hole (BH). The lack of a redshifted wing in the line poses a lower
limit of >40 rg for its distance from the BH. The Fe Kalpha could thus be
emitted from the inner regions of the BLR, i.e. within the ~80 light days
indicated by the Hbeta line measurements. In addition to these two neutral Fe
Kalpha components, we confirm the detection of weak (EW~8-20 eV) ionised Fe K
emission. This ionised line can be modeled with either a blend of two narrow
FeXXV and FeXXVI emission lines or with a single relativistic line produced, in
an ionised disc, down to a few rg from the BH. Finally, we observe a
weakening/disappearing of the medium and high velocity high ionisation Fe K
wind features found in previous XMM-Newton observations. This campaign has made
possible the first reverberation measurement of the resolved component of the
Fe Kalpha line, from which we can infer a location for the bulk of its emission
at a distance of r~40-1000 rg from the BH.
A filament of dark matter between two clusters of galaxies. (arXiv:1207.0809v1 [astro-ph.CO])
A filament of dark matter between two clusters of galaxies. (arXiv:1207.0809v1 [astro-ph.CO]):
It is a firm prediction of the concordance Cold Dark Matter (CDM)
cosmological model that galaxy clusters live at the intersection of large-scale
structure filaments. The thread-like structure of this "cosmic web" has been
traced by galaxy redshift surveys for decades. More recently the Warm-Hot
Intergalactic Medium (WHIM) residing in low redshift filaments has been
observed in emission and absorption. However, a reliable direct detection of
the underlying Dark Matter skeleton, which should contain more than half of all
matter, remained elusive, as earlier candidates for such detections were either
falsified or suffered from low signal-to-noise ratios and unphysical
misalignements of dark and luminous matter. Here we report the detection of a
dark matter filament connecting the two main components of the Abell 222/223
supercluster system from its weak gravitational lensing signal, both in a
non-parametric mass reconstruction and in parametric model fits. This filament
is coincident with an overdensity of galaxies and diffuse, soft X-ray emission
and contributes mass comparable to that of an additional galaxy cluster to the
total mass of the supercluster. Combined with X-ray observations, we place an
upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas
divided by the total mass, in the filament.
It is a firm prediction of the concordance Cold Dark Matter (CDM)
cosmological model that galaxy clusters live at the intersection of large-scale
structure filaments. The thread-like structure of this "cosmic web" has been
traced by galaxy redshift surveys for decades. More recently the Warm-Hot
Intergalactic Medium (WHIM) residing in low redshift filaments has been
observed in emission and absorption. However, a reliable direct detection of
the underlying Dark Matter skeleton, which should contain more than half of all
matter, remained elusive, as earlier candidates for such detections were either
falsified or suffered from low signal-to-noise ratios and unphysical
misalignements of dark and luminous matter. Here we report the detection of a
dark matter filament connecting the two main components of the Abell 222/223
supercluster system from its weak gravitational lensing signal, both in a
non-parametric mass reconstruction and in parametric model fits. This filament
is coincident with an overdensity of galaxies and diffuse, soft X-ray emission
and contributes mass comparable to that of an additional galaxy cluster to the
total mass of the supercluster. Combined with X-ray observations, we place an
upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas
divided by the total mass, in the filament.
By Dawn's Early Light: CMB Polarization Impact on Cosmological Constraints. (arXiv:1207.1105v2 [astro-ph.CO] UPDATED)
By Dawn's Early Light: CMB Polarization Impact on Cosmological Constraints. (arXiv:1207.1105v2 [astro-ph.CO] UPDATED):
Cosmic microwave background polarization encodes information not only on the
early universe but also dark energy, neutrino mass, and gravity in the late
universe through CMB lensing. Ground based surveys such as ACTpol, PolarBear,
SPTpol significantly complement cosmological constraints from the Planck
satellite, strengthening the CMB dark energy figure of merit and neutrino mass
constraints by factors of 3-4. This changes the dark energy probe landscape. We
evaluate the state of knowledge in 2017 from ongoing experiments including dark
energy surveys (supernovae, weak lensing, galaxy clustering), fitting for
dynamical dark energy, neutrino mass, and a modified gravitational growth
index. Adding a modest strong lensing time delay survey improves those dark
energy constraints by a further 32%, and an enhanced low redshift supernova
program improves them by 26%.
Cosmic microwave background polarization encodes information not only on the
early universe but also dark energy, neutrino mass, and gravity in the late
universe through CMB lensing. Ground based surveys such as ACTpol, PolarBear,
SPTpol significantly complement cosmological constraints from the Planck
satellite, strengthening the CMB dark energy figure of merit and neutrino mass
constraints by factors of 3-4. This changes the dark energy probe landscape. We
evaluate the state of knowledge in 2017 from ongoing experiments including dark
energy surveys (supernovae, weak lensing, galaxy clustering), fitting for
dynamical dark energy, neutrino mass, and a modified gravitational growth
index. Adding a modest strong lensing time delay survey improves those dark
energy constraints by a further 32%, and an enhanced low redshift supernova
program improves them by 26%.
Tidal interaction vs. ram pressure stripping effects as seen in X-rays. Hot gas in group and cluster galaxies. (arXiv:1207.1684v1 [astro-ph.CO])
Tidal interaction vs. ram pressure stripping effects as seen in X-rays. Hot gas in group and cluster galaxies. (arXiv:1207.1684v1 [astro-ph.CO]):
The hot intracluster/intragroup medium (ICM/IGM) and a high galaxy density
can lead to perturbations of the galactic interstellar medium (ISM) due to ram
pressure and/or tidal interaction effects. In radio polarimetry observations,
both phenomena may manifest similar features. X-ray data can help to determine
the real origin of the perturbation. We analyse the distribution and physical
properties of the hot gas in the Virgo cluster spiral galaxies NGC 4254 and NGC
4569, which indicate that the cluster environment has had a significant
influence on their properties. By performing both spatial and spectral analyses
of X-ray data, we try to distinguish between two major phenomena: tidal and ram
pressure interactions. We compare our findings with the case of NGC 2276, in
which a shock was reported, by analysing XMM-Newton X-ray data for this galaxy.
We use archival XMM-Newton observations of NGC 4254, NGC 4569, and NGC 2276.
Maps of the soft diffuse emission in the energy band 0.2 - 1 keV are obtained.
For the three galaxies, especially at the position of magnetic field
enhancements we perform a spectral analysis to derive gas temperatures and thus
to look for shock signatures. A shock is a signature of ram pressure resulting
from supersonic velocities; weak tidal interactions are not expected to
influence the temperature of the ionized gas. In NGC 4254, we do not observe
any temperature increase. This suggests tidal interactions rather than ram
pressure stripping. In NGC 4569 the radio polarized ridge shows a higher
temperature, which may indicate ram-pressure effects. For NGC 2276, we do not
find clear indications of a shock. The main driver of the observed distortions
is most likely tidal interaction. Determining gas temperatures via sensitive
X-ray observations seems to be a good method for distinguishing between ram
pressure and tidal interaction effects acting upon a galaxy.
The hot intracluster/intragroup medium (ICM/IGM) and a high galaxy density
can lead to perturbations of the galactic interstellar medium (ISM) due to ram
pressure and/or tidal interaction effects. In radio polarimetry observations,
both phenomena may manifest similar features. X-ray data can help to determine
the real origin of the perturbation. We analyse the distribution and physical
properties of the hot gas in the Virgo cluster spiral galaxies NGC 4254 and NGC
4569, which indicate that the cluster environment has had a significant
influence on their properties. By performing both spatial and spectral analyses
of X-ray data, we try to distinguish between two major phenomena: tidal and ram
pressure interactions. We compare our findings with the case of NGC 2276, in
which a shock was reported, by analysing XMM-Newton X-ray data for this galaxy.
We use archival XMM-Newton observations of NGC 4254, NGC 4569, and NGC 2276.
Maps of the soft diffuse emission in the energy band 0.2 - 1 keV are obtained.
For the three galaxies, especially at the position of magnetic field
enhancements we perform a spectral analysis to derive gas temperatures and thus
to look for shock signatures. A shock is a signature of ram pressure resulting
from supersonic velocities; weak tidal interactions are not expected to
influence the temperature of the ionized gas. In NGC 4254, we do not observe
any temperature increase. This suggests tidal interactions rather than ram
pressure stripping. In NGC 4569 the radio polarized ridge shows a higher
temperature, which may indicate ram-pressure effects. For NGC 2276, we do not
find clear indications of a shock. The main driver of the observed distortions
is most likely tidal interaction. Determining gas temperatures via sensitive
X-ray observations seems to be a good method for distinguishing between ram
pressure and tidal interaction effects acting upon a galaxy.
EoS for massive neutron stars. (arXiv:1207.1554v1 [astro-ph.SR])
EoS for massive neutron stars. (arXiv:1207.1554v1 [astro-ph.SR]):
Using relativistic Hartree-Fock approximation, we investigate the properties
of the neutron-star matter in detail. In the present calculation, we consider
not only the tensor coupling of vector mesons to octet baryons and the form
factors at interaction vertexes but also the internal (quark) structure change
of baryons in dense matter. The relativistic Hartree-Fock calculations are
performed in two ways: one is the calculation with the coupling constants
determined by SU(6) (quark model) symmetry, the other is with the coupling
constants based on SU(3) (flavor) symmetry. For the latter case, we use the
latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle
composition of the core matter in SU(3) symmetry is completely different from
that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the
density region below $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the
\Xi^- hyperon is produced. Furthermore, the medium modification of the internal
baryon structure hardens the equation of state for the core matter. Taking all
these effects into account, we can obtain the maximum neutron-star mass which
is consistent with the recently observed mass, 1.97 \pm 0.04 M_\sun (PSR
J1614-2230). We therefore conclude that the extension from SU(6) symmetry to
SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure
variation in matter certainly enhance the mass of neutron star. Furthermore,
the effects of the form factor at vertex and the Fock contribution including
the tensor coupling due to the vector mesons are indispensable to describe the
core matter. In particular, the Fock term is very vital in reproducing the
preferable value of symmetry energy, a_4 (\simeq 30 - 40 MeV), in nuclear
matter.
Using relativistic Hartree-Fock approximation, we investigate the properties
of the neutron-star matter in detail. In the present calculation, we consider
not only the tensor coupling of vector mesons to octet baryons and the form
factors at interaction vertexes but also the internal (quark) structure change
of baryons in dense matter. The relativistic Hartree-Fock calculations are
performed in two ways: one is the calculation with the coupling constants
determined by SU(6) (quark model) symmetry, the other is with the coupling
constants based on SU(3) (flavor) symmetry. For the latter case, we use the
latest Nijmegen (ESC08) model. Then, it is very remarkable that the particle
composition of the core matter in SU(3) symmetry is completely different from
that in SU(6) symmetry. In SU(6) symmetry, all octet baryons appear in the
density region below $\sim 1.2$ fm$^{-3}$, while, in the ESC08 model, only the
\Xi^- hyperon is produced. Furthermore, the medium modification of the internal
baryon structure hardens the equation of state for the core matter. Taking all
these effects into account, we can obtain the maximum neutron-star mass which
is consistent with the recently observed mass, 1.97 \pm 0.04 M_\sun (PSR
J1614-2230). We therefore conclude that the extension from SU(6) symmetry to
SU(3) symmetry in the meson-baryon couplings and the internal baryon-structure
variation in matter certainly enhance the mass of neutron star. Furthermore,
the effects of the form factor at vertex and the Fock contribution including
the tensor coupling due to the vector mesons are indispensable to describe the
core matter. In particular, the Fock term is very vital in reproducing the
preferable value of symmetry energy, a_4 (\simeq 30 - 40 MeV), in nuclear
matter.
The X-ray lightcurve of Sgr A* over the past 150 years inferred from Fe-Ka line reverberation in Galactic Centre molecular clouds. (arXiv:1207.1436v1 [astro-ph.HE])
The X-ray lightcurve of Sgr A* over the past 150 years inferred from Fe-Ka line reverberation in Galactic Centre molecular clouds. (arXiv:1207.1436v1 [astro-ph.HE]):
We examine the temporal and spectral properties of nine Fe-Ka bright
molecular clouds within about 30 pc of Sgr A*, in order to understand and
constrain the primary energising source of the Fe fluorescence. Significant
Fe-Ka variability was detected, with a spatial and temporal pattern consistent
with that reported in previous studies. The main breakthrough that sets our
paper apart from earlier contributions on this topic is the direct measurement
of the column density and the Fe abundance of the MCs in our sample. We used
the EW measurements to infer the average Fe abundance within the clouds to be
1.6$\pm$0.1 times solar. The cloud column densities derived from the spectral
analysis were typically of the order of 10$^{23}$ cm$^{-2}$, which is
significantly higher than previous estimates. This in turn has a significant
impact on the inferred geometry and time delays within the cloud system. Past
X-ray activity of Sgr A* is the most likely source of ionisation within the
molecular clouds in the innermost 30 pc of the Galaxy. In this scenario, the
X-ray luminosity required to excite these reflection nebulae is of the order of
10$^{37}-10^{38}$ erg s$^{-1}$, significantly lower than that estimated for the
Sgr B2 molecular cloud. Moreover, the inferred Sgr A* lightcurve over the past
150 years shows a long-term downwards trend punctuated by occasional
counter-trend brightening episodes of at least 5 years duration. Finally, we
found that contributions to the Fe fluorescence by X-ray transient binaries and
cosmic-ray bombardment are very likely, and suggest possible ways to study this
latter phenomenon in the near future.
We examine the temporal and spectral properties of nine Fe-Ka bright
molecular clouds within about 30 pc of Sgr A*, in order to understand and
constrain the primary energising source of the Fe fluorescence. Significant
Fe-Ka variability was detected, with a spatial and temporal pattern consistent
with that reported in previous studies. The main breakthrough that sets our
paper apart from earlier contributions on this topic is the direct measurement
of the column density and the Fe abundance of the MCs in our sample. We used
the EW measurements to infer the average Fe abundance within the clouds to be
1.6$\pm$0.1 times solar. The cloud column densities derived from the spectral
analysis were typically of the order of 10$^{23}$ cm$^{-2}$, which is
significantly higher than previous estimates. This in turn has a significant
impact on the inferred geometry and time delays within the cloud system. Past
X-ray activity of Sgr A* is the most likely source of ionisation within the
molecular clouds in the innermost 30 pc of the Galaxy. In this scenario, the
X-ray luminosity required to excite these reflection nebulae is of the order of
10$^{37}-10^{38}$ erg s$^{-1}$, significantly lower than that estimated for the
Sgr B2 molecular cloud. Moreover, the inferred Sgr A* lightcurve over the past
150 years shows a long-term downwards trend punctuated by occasional
counter-trend brightening episodes of at least 5 years duration. Finally, we
found that contributions to the Fe fluorescence by X-ray transient binaries and
cosmic-ray bombardment are very likely, and suggest possible ways to study this
latter phenomenon in the near future.
Half-Skyrmions and the Equation of State for Compact-Star Matter. (arXiv:1207.0429v1 [nucl-th] CROSS LISTED)
Half-Skyrmions and the Equation of State for Compact-Star Matter. (arXiv:1207.0429v1 [nucl-th] CROSS LISTED):
The half-skyrmions that appear in dense baryonic matter when skyrmions are
put on crystals modify drastically hadron properties in dense medium and affect
strongly the nuclear tensor forces, thereby influencing the equation of state
(EoS) of dense nuclear and asymmetric nuclear matter. The matter comprised of
half skyrmions has vanishing quark condensate but non-vanishing pion decay
constant and could be interpreted as a hadronic dual of strong-coupled quark
matter. We infer from this observation a set of new scaling laws -- called
"new-BR" -- for the parameters in nuclear effective field theory controlled by
renormalization-group flow. They are subjected to the EoS of symmetric and
asymmetric nuclear matter, and are then applied to nuclear symmetry energies
and properties of compact stars. The changeover from the skyrmion matter to a
half-skyrmion matter that takes place after the cross-over density $n_{1/2}$
makes the EoS stiffer and leads to a compact star as massive as $\sim
2.4M_\odot$. Cross-over density in the range $ 1.5n_0 \lsim n_{1/2} \lsim 2.0
n_0$ has been employed, and the differences between the EoSs before and after
this density and the dependence of our results on $n_{1/2}$ are discussed. The
novel structure of the EoS obtained with the new-BR scaling is relevant for
neutron-rich nuclei and compact star matter and could be studied in RIB (rare
isotope beam) machines.
The half-skyrmions that appear in dense baryonic matter when skyrmions are
put on crystals modify drastically hadron properties in dense medium and affect
strongly the nuclear tensor forces, thereby influencing the equation of state
(EoS) of dense nuclear and asymmetric nuclear matter. The matter comprised of
half skyrmions has vanishing quark condensate but non-vanishing pion decay
constant and could be interpreted as a hadronic dual of strong-coupled quark
matter. We infer from this observation a set of new scaling laws -- called
"new-BR" -- for the parameters in nuclear effective field theory controlled by
renormalization-group flow. They are subjected to the EoS of symmetric and
asymmetric nuclear matter, and are then applied to nuclear symmetry energies
and properties of compact stars. The changeover from the skyrmion matter to a
half-skyrmion matter that takes place after the cross-over density $n_{1/2}$
makes the EoS stiffer and leads to a compact star as massive as $\sim
2.4M_\odot$. Cross-over density in the range $ 1.5n_0 \lsim n_{1/2} \lsim 2.0
n_0$ has been employed, and the differences between the EoSs before and after
this density and the dependence of our results on $n_{1/2}$ are discussed. The
novel structure of the EoS obtained with the new-BR scaling is relevant for
neutron-rich nuclei and compact star matter and could be studied in RIB (rare
isotope beam) machines.
Dynamic of the accelerated expansion of the universe in the DGP model. (arXiv:1207.2365v1 [astro-ph.CO])
Dynamic of the accelerated expansion of the universe in the DGP model. (arXiv:1207.2365v1 [astro-ph.CO]):
According to experimental data of SNe Ia (Supernovae type Ia), we will
discuss in detial dynamics of the DGP model and introduce a simple
parametrization of matter $\omega$, in order to analyze scenarios of the
expanding universe and the evolution of the scale factor. We find that the
dimensionless matter density parameter at the present epoch $\Omega^0_m=0.3$,
the age of the universe $t_0= 12.48$ Gyr,
$\frac{a}{a_0}=-2.4e^{\frac{-t}{25.56}}+2.45$. The next we study the linear
growth of matter perturbations, and we assume a definition of the growth rate,
$f \equiv \frac{dln\delta}{dlna}$. As many authors for many years, we have been
using a good approximation to the growth rate $f \approx \Omega^{\gamma(z)}_m$,
we also find that the best fit of the growth index, $\gamma(z)\approx 0.687 -
\frac{40.67}{1 + e^{1.7. (4.48 + z)}}$, or $\gamma(z)= 0.667 + 0.033z$ when
$z\ll1$. We also compare the age of the universe and the growth index with
other models and experimental data. We can see that the DGP model describes the
cosmic acceleration as well as other models that usually refers to dark energy
and Cold Dark Matter (CDM).
According to experimental data of SNe Ia (Supernovae type Ia), we will
discuss in detial dynamics of the DGP model and introduce a simple
parametrization of matter $\omega$, in order to analyze scenarios of the
expanding universe and the evolution of the scale factor. We find that the
dimensionless matter density parameter at the present epoch $\Omega^0_m=0.3$,
the age of the universe $t_0= 12.48$ Gyr,
$\frac{a}{a_0}=-2.4e^{\frac{-t}{25.56}}+2.45$. The next we study the linear
growth of matter perturbations, and we assume a definition of the growth rate,
$f \equiv \frac{dln\delta}{dlna}$. As many authors for many years, we have been
using a good approximation to the growth rate $f \approx \Omega^{\gamma(z)}_m$,
we also find that the best fit of the growth index, $\gamma(z)\approx 0.687 -
\frac{40.67}{1 + e^{1.7. (4.48 + z)}}$, or $\gamma(z)= 0.667 + 0.033z$ when
$z\ll1$. We also compare the age of the universe and the growth index with
other models and experimental data. We can see that the DGP model describes the
cosmic acceleration as well as other models that usually refers to dark energy
and Cold Dark Matter (CDM).
High-Frequency Quasi-Periodic Oscillations in black-hole binaries. (arXiv:1207.2311v1 [astro-ph.HE])
High-Frequency Quasi-Periodic Oscillations in black-hole binaries. (arXiv:1207.2311v1 [astro-ph.HE]):
We present the results of the analysis of a large database of X-ray
observations of 22 galactic black-hole transients with the Rossi X-Ray timing
explorer throughout its operative life for a total exposure time of ~12 Ms. We
excluded persistent systems and the peculiar source GRS 1915+105, as well as
the most recently discovered sources. The semi-automatic homogeneous analysis
was aimed at the detection of high-frequency (100-1000 Hz) quasi-periodic
oscillations (QPO), of which several cases were previously reported in the
literature. After taking into account the number of independent trials, we
obtained 11 detections from two sources only: XTE J1550-564 and GRO J1655-40.
For the former, the detected frequencies are clustered around 180 Hz and 280
Hz, as previously found. For the latter, the previously-reported dichotomy
300-450 Hz is found to be less sharp. We discuss our results in comparison with
kHz QPO in neutron-star X-ray binaries and the prospects for future timing
X-ray missions.
We present the results of the analysis of a large database of X-ray
observations of 22 galactic black-hole transients with the Rossi X-Ray timing
explorer throughout its operative life for a total exposure time of ~12 Ms. We
excluded persistent systems and the peculiar source GRS 1915+105, as well as
the most recently discovered sources. The semi-automatic homogeneous analysis
was aimed at the detection of high-frequency (100-1000 Hz) quasi-periodic
oscillations (QPO), of which several cases were previously reported in the
literature. After taking into account the number of independent trials, we
obtained 11 detections from two sources only: XTE J1550-564 and GRO J1655-40.
For the former, the detected frequencies are clustered around 180 Hz and 280
Hz, as previously found. For the latter, the previously-reported dichotomy
300-450 Hz is found to be less sharp. We discuss our results in comparison with
kHz QPO in neutron-star X-ray binaries and the prospects for future timing
X-ray missions.
Core-collapse supernova equations of state based on neutron star observations. (arXiv:1207.2184v1 [astro-ph.SR])
Core-collapse supernova equations of state based on neutron star observations. (arXiv:1207.2184v1 [astro-ph.SR]):
Many of the currently available equations of state for core-collapse
supernova simulations give large neutron star radii and do not provide large
enough neutron star masses, both of which are inconsistent with some recent
neutron star observations. In addition, one of the critical uncertainties in
the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully
explored by the currently available equations of state. In this article, we
construct two new equations of state which match recent neutron star
observations and provide more flexibility in studying the dependence on nuclear
matter properties. The equations of state are also provided in tabular form,
covering a wide range in density, temperature and asymmetry, suitable for
astrophysical simulations. These new equations of state are implemented into
our spherically symmetric core-collapse supernova model, which is based on
general relativistic radiation hydrodynamics with three-flavor Boltzmann
neutrino transport. The results are compared with commonly used equations of
state in supernova simulations of 15 and 40 solar mass progenitors. We do not
find any simple correlations between individual nuclear matter properties at
saturation and the outcome of these simulations. However, the new equations of
state lead to the most compact neutron stars among the relativistic mean-field
models which we considered. The new models also obey the previously observed
correlation between the time to black hole formation and the maximum mass of an
s=4 neutron star.
Many of the currently available equations of state for core-collapse
supernova simulations give large neutron star radii and do not provide large
enough neutron star masses, both of which are inconsistent with some recent
neutron star observations. In addition, one of the critical uncertainties in
the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully
explored by the currently available equations of state. In this article, we
construct two new equations of state which match recent neutron star
observations and provide more flexibility in studying the dependence on nuclear
matter properties. The equations of state are also provided in tabular form,
covering a wide range in density, temperature and asymmetry, suitable for
astrophysical simulations. These new equations of state are implemented into
our spherically symmetric core-collapse supernova model, which is based on
general relativistic radiation hydrodynamics with three-flavor Boltzmann
neutrino transport. The results are compared with commonly used equations of
state in supernova simulations of 15 and 40 solar mass progenitors. We do not
find any simple correlations between individual nuclear matter properties at
saturation and the outcome of these simulations. However, the new equations of
state lead to the most compact neutron stars among the relativistic mean-field
models which we considered. The new models also obey the previously observed
correlation between the time to black hole formation and the maximum mass of an
s=4 neutron star.
X-ray emission from star-forming galaxies - III. Calibration of the Lx-SFR relation up to redshift z$\simeq$1.3. (arXiv:1207.2157v1 [astro-ph.HE])
X-ray emission from star-forming galaxies - III. Calibration of the Lx-SFR relation up to redshift z$\simeq$1.3. (arXiv:1207.2157v1 [astro-ph.HE]):
We investigate the relation between total X-ray emission from star-forming
galaxies and their star formation activity. Using nearby late-type galaxies and
ULIRGs from Paper I and star-forming galaxies from Chandra Deep Fields, we
construct a sample of 54 galaxies spanning the redshift range z\approx0-1.3 and
the SFR range ~0.1-10^{3} Msun/yr. In agreement with previous results, we find
that the Lx-SFR relation is consistent with a linear law both at z=0 and for
the z=0.1-1.3 CDF galaxies, within the statistical accuracy of ~0.1 in the
slope of the Lx-SFR relation. For the total sample, we find a linear scaling
relation Lx/SFR\approx(3.5\pm0.4)\times10^{39}(erg/s)/(Msun/yr), with a scatter
of \approx0.4 dex. About ~3/4 of the 0.5-8 keV luminosity generated per unit
SFR is provided by HMXBs. We find no statistically significant trends in the
Lx/SFR ratio with the redshift or star formation rate and constrain the
amplitude of its variations by \lesssim0.1-0.2 dex. These properties make X-ray
observations a powerful tool to measure the star formation rate in normal
star-forming galaxies that dominate the source counts at faint fluxes.
We investigate the relation between total X-ray emission from star-forming
galaxies and their star formation activity. Using nearby late-type galaxies and
ULIRGs from Paper I and star-forming galaxies from Chandra Deep Fields, we
construct a sample of 54 galaxies spanning the redshift range z\approx0-1.3 and
the SFR range ~0.1-10^{3} Msun/yr. In agreement with previous results, we find
that the Lx-SFR relation is consistent with a linear law both at z=0 and for
the z=0.1-1.3 CDF galaxies, within the statistical accuracy of ~0.1 in the
slope of the Lx-SFR relation. For the total sample, we find a linear scaling
relation Lx/SFR\approx(3.5\pm0.4)\times10^{39}(erg/s)/(Msun/yr), with a scatter
of \approx0.4 dex. About ~3/4 of the 0.5-8 keV luminosity generated per unit
SFR is provided by HMXBs. We find no statistically significant trends in the
Lx/SFR ratio with the redshift or star formation rate and constrain the
amplitude of its variations by \lesssim0.1-0.2 dex. These properties make X-ray
observations a powerful tool to measure the star formation rate in normal
star-forming galaxies that dominate the source counts at faint fluxes.
Athena (Advanced Telescope for High ENergy Astrophysics) Assessment Study Report for ESA Cosmic Vision 2015-2025. (arXiv:1207.2745v1 [astro-ph.HE])
Athena (Advanced Telescope for High ENergy Astrophysics) Assessment Study Report for ESA Cosmic Vision 2015-2025. (arXiv:1207.2745v1 [astro-ph.HE]):
Athena is an X-ray observatory-class mission concept, developed from April to
December 2011 as a result of the reformulation exercise for L-class mission
proposals in the framework of ESA's Cosmic Vision 2015-2025. Athena's science
case is that of the Universe of extremes, from Black Holes to Large-scale
structure. The specific science goals are structured around three main pillars:
"Black Holes and accretion physics", "Cosmic feedback" and "Large-scale
structure of the Universe". Underpinning these pillars, the study of hot
astrophysical plasmas offered by Athena broadens its scope to virtually all
corners of Astronomy. The Athena concept consists of two co-aligned X-ray
telescopes, with focal length 12 m, angular resolution of 10" or better, and
totalling an effective area of 1 m2 at 1 keV (0.5 m2 at 6 keV). At the focus of
one of the telescopes there is a Wide Field Imager (WFI) providing a field of
view of 24'\times 24', 150 eV spectral resolution at 6 keV, and high count rate
capability. At the focus of the other telescope there is the X-ray
Microcalorimeter Spectrometer (XMS), a cryogenic instrument offering a spectral
resolution of 3 eV over a field of view of 2.3' \times 2.3'. Although Athena
has not been selected as ESA's Cosmic Vision 2015-2025 L1 mission, its science
goals and concept conform the basis of what should become ESA's X-ray astronomy
flagship.
Athena is an X-ray observatory-class mission concept, developed from April to
December 2011 as a result of the reformulation exercise for L-class mission
proposals in the framework of ESA's Cosmic Vision 2015-2025. Athena's science
case is that of the Universe of extremes, from Black Holes to Large-scale
structure. The specific science goals are structured around three main pillars:
"Black Holes and accretion physics", "Cosmic feedback" and "Large-scale
structure of the Universe". Underpinning these pillars, the study of hot
astrophysical plasmas offered by Athena broadens its scope to virtually all
corners of Astronomy. The Athena concept consists of two co-aligned X-ray
telescopes, with focal length 12 m, angular resolution of 10" or better, and
totalling an effective area of 1 m2 at 1 keV (0.5 m2 at 6 keV). At the focus of
one of the telescopes there is a Wide Field Imager (WFI) providing a field of
view of 24'\times 24', 150 eV spectral resolution at 6 keV, and high count rate
capability. At the focus of the other telescope there is the X-ray
Microcalorimeter Spectrometer (XMS), a cryogenic instrument offering a spectral
resolution of 3 eV over a field of view of 2.3' \times 2.3'. Although Athena
has not been selected as ESA's Cosmic Vision 2015-2025 L1 mission, its science
goals and concept conform the basis of what should become ESA's X-ray astronomy
flagship.
X-ray Spectra from MHD Simulations of Accreting Black Holes. (arXiv:1207.2693v1 [astro-ph.HE])
X-ray Spectra from MHD Simulations of Accreting Black Holes. (arXiv:1207.2693v1 [astro-ph.HE]):
We present the results of a new global radiation transport code coupled to a
general relativistic magneto-hydrodynamic simulation of an accreting,
non-rotating black hole. For the first time, we are able to predict in a
self-consistent way the X-ray spectra observed from stellar-mass black holes,
including a thermal peak, Compton reflection hump, power-law tail, and broad
iron line. Varying only the mass accretion rate, we are able to reproduce the
low/hard, steep power-law, and thermal-dominant states seen in most galactic
black hole sources. The temperature in the corona is T_e ~ 10 keV in a boundary
layer near the disk and rises smoothly to T_e >~ 100 keV in low-density regions
far above the disk. Even as the disk's reflection edge varies from the horizon
out to ~6M as the accretion rate decreases, we find that the shape of the Fe
K\alpha line is remarkably constant. This is because photons emitted from the
plunging region are strongly beamed into the horizon and never reach the
observer. We have also carried out a basic timing analysis of the spectra and
find that the fractional variability increases with photon energy and viewer
inclination angle, consistent with the coronal hot spot model for X-ray
fluctuations.
We present the results of a new global radiation transport code coupled to a
general relativistic magneto-hydrodynamic simulation of an accreting,
non-rotating black hole. For the first time, we are able to predict in a
self-consistent way the X-ray spectra observed from stellar-mass black holes,
including a thermal peak, Compton reflection hump, power-law tail, and broad
iron line. Varying only the mass accretion rate, we are able to reproduce the
low/hard, steep power-law, and thermal-dominant states seen in most galactic
black hole sources. The temperature in the corona is T_e ~ 10 keV in a boundary
layer near the disk and rises smoothly to T_e >~ 100 keV in low-density regions
far above the disk. Even as the disk's reflection edge varies from the horizon
out to ~6M as the accretion rate decreases, we find that the shape of the Fe
K\alpha line is remarkably constant. This is because photons emitted from the
plunging region are strongly beamed into the horizon and never reach the
observer. We have also carried out a basic timing analysis of the spectra and
find that the fractional variability increases with photon energy and viewer
inclination angle, consistent with the coronal hot spot model for X-ray
fluctuations.
Neutrino-driven wind simulations and nucleosynthesis of heavy elements. (arXiv:1207.2527v1 [astro-ph.SR])
Neutrino-driven wind simulations and nucleosynthesis of heavy elements. (arXiv:1207.2527v1 [astro-ph.SR]):
Neutrino-driven winds, which follow core-collapse supernova explosions,
present a fascinating nuclear astrophysics problem that requires understanding
advanced astrophysics simulations, the properties of matter and neutrino
interactions under extreme conditions, the structure and reactions of exotic
nuclei, and comparisons against forefront astronomical observations. The
neutrino-driven wind has attracted vast attention over the last 20 years as it
was suggested to be a candidate for the astrophysics site where half of the
heavy elements are produced via the r-process. In this review, we summarize our
present understanding of neutrino-driven winds from the dynamical and
nucleosynthesis perspectives. Rapid progress has been made during recent years
in understanding the wind with improved simulations and better micro physics.
The current status of the fields is that hydrodynamical simulations do not
reach the extreme conditions necessary for the r-process and the proton or
neutron richness of the wind remains to be investigated in more detail.
However, nucleosynthesis studies and observations point already to
neutrino-driven winds to explain the origin of lighter heavy elements, such as
Sr, Y, Zr.
Neutrino-driven winds, which follow core-collapse supernova explosions,
present a fascinating nuclear astrophysics problem that requires understanding
advanced astrophysics simulations, the properties of matter and neutrino
interactions under extreme conditions, the structure and reactions of exotic
nuclei, and comparisons against forefront astronomical observations. The
neutrino-driven wind has attracted vast attention over the last 20 years as it
was suggested to be a candidate for the astrophysics site where half of the
heavy elements are produced via the r-process. In this review, we summarize our
present understanding of neutrino-driven winds from the dynamical and
nucleosynthesis perspectives. Rapid progress has been made during recent years
in understanding the wind with improved simulations and better micro physics.
The current status of the fields is that hydrodynamical simulations do not
reach the extreme conditions necessary for the r-process and the proton or
neutron richness of the wind remains to be investigated in more detail.
However, nucleosynthesis studies and observations point already to
neutrino-driven winds to explain the origin of lighter heavy elements, such as
Sr, Y, Zr.
Some constraints on the lower mass limit for double-degenerate progenitors of Type Ia supernovae. (arXiv:1207.2519v1 [astro-ph.SR])
Some constraints on the lower mass limit for double-degenerate progenitors of Type Ia supernovae. (arXiv:1207.2519v1 [astro-ph.SR]):
Recent theoretical and observational studies both argue that the merging of
double carbon-oxygen white dwarfs (WDs) is responsible for at least some Type
Ia supernovae (SNe Ia). Previous (standard) studies of the anticipated SN
birthrate from this channel have assumed that the merger process is
conservative and that the primary criterion for explosion is that the merged
mass exceeds the Chandrasekhar mass. Han & Webbink (1999) demonstrated that
mass transfer and merger in close double WDs will in many cases be
non-conservative. Pakmor et al. (2011) further suggested that the merger
process should be violent in order to initiate an explosion. We have therefore
investigated how the SN Ia birthrate from the double-degenerate (DD) channel is
affected by these constraints. Using the binary-star population-synthesis
method, we have calculated the DD SN Ia birthrate under conservative and
non-conservative approximations, and including lower mass and mass-ratio limits
indicated by recent smoothed-particle-hydrodynamic calculations. The predicted
DD SN Ia rate is significantly reduced by all of these constraints. With
dynamical mass loss alone (violent merger) the birthrate is reduced to 56% of
the conservative rate. Requiring that the mass ratio $q>2/3$ further reduces
the birthrate to 18% that of the standard assumption. An upper limit of 0.0061
SNuM, or a Galactic rate of $4.6 \times 10^{-4}{\rm yr}^{-1}$, might be
realistic.
Recent theoretical and observational studies both argue that the merging of
double carbon-oxygen white dwarfs (WDs) is responsible for at least some Type
Ia supernovae (SNe Ia). Previous (standard) studies of the anticipated SN
birthrate from this channel have assumed that the merger process is
conservative and that the primary criterion for explosion is that the merged
mass exceeds the Chandrasekhar mass. Han & Webbink (1999) demonstrated that
mass transfer and merger in close double WDs will in many cases be
non-conservative. Pakmor et al. (2011) further suggested that the merger
process should be violent in order to initiate an explosion. We have therefore
investigated how the SN Ia birthrate from the double-degenerate (DD) channel is
affected by these constraints. Using the binary-star population-synthesis
method, we have calculated the DD SN Ia birthrate under conservative and
non-conservative approximations, and including lower mass and mass-ratio limits
indicated by recent smoothed-particle-hydrodynamic calculations. The predicted
DD SN Ia rate is significantly reduced by all of these constraints. With
dynamical mass loss alone (violent merger) the birthrate is reduced to 56% of
the conservative rate. Requiring that the mass ratio $q>2/3$ further reduces
the birthrate to 18% that of the standard assumption. An upper limit of 0.0061
SNuM, or a Galactic rate of $4.6 \times 10^{-4}{\rm yr}^{-1}$, might be
realistic.
The VMC Survey - VI. Quasars behind the Magellanic system. (arXiv:1207.2492v1 [astro-ph.CO])
The VMC Survey - VI. Quasars behind the Magellanic system. (arXiv:1207.2492v1 [astro-ph.CO]):
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for studies of proper motion and of the
interstellar medium along the line of sight. We search for criteria to identify
candidate QSOs using near-infrared observations from the VISTA survey of the
Magellanic Clouds system (VMC). The VMC survey provides photometry in the YJKs
bands and 12 epochs in the Ks band with unprecedented sensitivity and spatial
resolution. The (Y-J) vs. (J-Ks) diagram has been used to distinguish QSOs from
Milky Way and Magellanic Cloud stars. Then, the slope of variation in the Ks
band has been used to identify a sample of high confidence candidates. These
criteria were developed based on the properties of 117 known QSOs. YJKs
magnitudes and Ks light-curves of known QSOs behind the Magellanic system from
present VMC data are presented. About 75% of them show a slope of variation
>10^-4 mag/day and the shape of the light-curve is in general irregular and
without any clear periodicity. A method to identify QSOs based solely on the
VMC data is proposed using YJKs colours and Ks variability. The number of QSO
candidates found in the South Ecliptic Pole and the 30 Doradus tiles is 22 and
26, respectively, with negligible contamination by young stellar objects,
planetary nebulae, stars and normal galaxies. The high confidence in the nature
of the selected objects is supported by recent studies of possible
contaminants, but remains to be confirmed spectroscopically. In the entire VMC
survey area we expect to find about 1500 QSOs behind the LMC, 600 behind the
SMC, 300 behind the Bridge and 50 behind the Stream areas. The Ks light-curves
can help support investigations of the mechanism responsible for the
variations. (Abridged)
The number and spatial distribution of confirmed quasi-stellar objects (QSOs)
behind the Magellanic system is limited. This undermines their use as
astrometric reference objects for studies of proper motion and of the
interstellar medium along the line of sight. We search for criteria to identify
candidate QSOs using near-infrared observations from the VISTA survey of the
Magellanic Clouds system (VMC). The VMC survey provides photometry in the YJKs
bands and 12 epochs in the Ks band with unprecedented sensitivity and spatial
resolution. The (Y-J) vs. (J-Ks) diagram has been used to distinguish QSOs from
Milky Way and Magellanic Cloud stars. Then, the slope of variation in the Ks
band has been used to identify a sample of high confidence candidates. These
criteria were developed based on the properties of 117 known QSOs. YJKs
magnitudes and Ks light-curves of known QSOs behind the Magellanic system from
present VMC data are presented. About 75% of them show a slope of variation
>10^-4 mag/day and the shape of the light-curve is in general irregular and
without any clear periodicity. A method to identify QSOs based solely on the
VMC data is proposed using YJKs colours and Ks variability. The number of QSO
candidates found in the South Ecliptic Pole and the 30 Doradus tiles is 22 and
26, respectively, with negligible contamination by young stellar objects,
planetary nebulae, stars and normal galaxies. The high confidence in the nature
of the selected objects is supported by recent studies of possible
contaminants, but remains to be confirmed spectroscopically. In the entire VMC
survey area we expect to find about 1500 QSOs behind the LMC, 600 behind the
SMC, 300 behind the Bridge and 50 behind the Stream areas. The Ks light-curves
can help support investigations of the mechanism responsible for the
variations. (Abridged)
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