Prompt Emission from Tidal Disruptions of White Dwarfs by Intermediate Mass Black Holes. (arXiv:1212.5267v1 [astro-ph.HE]):
We present a qualitative picture of prompt emission from tidal disruptions of
white dwarfs (WD) by intermediate mass black holes (IMBH). The smaller size of
an IMBH compared to a supermassive black hole and a smaller tidal radius of a
WD disruption lead to a very fast event with high peak luminosity. Magnetic
field is generated in situ following the tidal disruption, which leads to
effective accretion. Since large-scale magnetic field is also produced,
geometrically thick super-Eddington inflow leads to a relativistic jet. The
dense jet possesses a photosphere, which emits quasi-thermal radiation in soft
X-rays. The source can be classified as a long low-luminosity gamma-ray burst
(ll-GRB). Tidal compression of a WD causes nuclear ignition, which is
observable as an accompanying supernova. We suggest that GRB060218 and SN2006aj
is such a pair of ll-GRB and supernova. We argue that in a flux-limited sample
the disruptions of WDs by IMBHs are more frequent then the disruptions of other
stars by IMBHs.
Wednesday, December 26, 2012
Saturday, December 22, 2012
Constraints on the symmetry energy from neutron star observations. (arXiv:1212.4539v1 [astro-ph.HE])
Constraints on the symmetry energy from neutron star observations. (arXiv:1212.4539v1 [astro-ph.HE]):
The modeling of many neutron star observables incorporates the microphysics
of both the stellar crust and core, which is tied intimately to the properties
of the nuclear matter equation of state (EoS). We explore the predictions of
such models over the range of experimentally constrained nuclear matter
parameters, focusing on the slope of the symmetry energy at nuclear saturation
density $L$. We use a consistent model of the composition and EoS of neutron
star crust and core matter to model the binding energy of pulsar B of the
double pulsar system J0737-3039, the frequencies of torsional oscillations of
the neutron star crust and the instability region for r-modes in the neutron
star core damped by electron-electron viscosity at the crust-core interface. By
confronting these models with observations, we illustrate the potential of
astrophysical observables to offer constraints on poorly known nuclear matter
parameters complementary to terrestrial experiments, and demonstrate that our
models consistently predict $L<70$ MeV.
The modeling of many neutron star observables incorporates the microphysics
of both the stellar crust and core, which is tied intimately to the properties
of the nuclear matter equation of state (EoS). We explore the predictions of
such models over the range of experimentally constrained nuclear matter
parameters, focusing on the slope of the symmetry energy at nuclear saturation
density $L$. We use a consistent model of the composition and EoS of neutron
star crust and core matter to model the binding energy of pulsar B of the
double pulsar system J0737-3039, the frequencies of torsional oscillations of
the neutron star crust and the instability region for r-modes in the neutron
star core damped by electron-electron viscosity at the crust-core interface. By
confronting these models with observations, we illustrate the potential of
astrophysical observables to offer constraints on poorly known nuclear matter
parameters complementary to terrestrial experiments, and demonstrate that our
models consistently predict $L<70$ MeV.
X-ray Emission from Strongly Asymmetric Circumstellar Material in the Remnant of Kepler's Supernova. (arXiv:1212.4534v1 [astro-ph.GA])
X-ray Emission from Strongly Asymmetric Circumstellar Material in the Remnant of Kepler's Supernova. (arXiv:1212.4534v1 [astro-ph.GA]):
Kepler's supernova remnant resulted from a thermonuclear explosion, but is
interacting with circumstellar material (CSM) lost from the progenitor system.
We describe a statistical technique for isolating X-ray emission due to CSM
from that due to shocked ejecta. Shocked CSM coincides well in position with 24
$\mu$m emission seen by {\sl Spitzer}. We find most CSM to be distributed along
the bright north rim, but substantial concentrations are also found projected
against the center of the remnant, roughly along a diameter with position angle
$\sim 100^\circ$. We interpret this as evidence for a disk distribution of CSM
before the SN, with the line of sight to the observer roughly in the disk
plane. We present 2-D hydrodynamic simulations of this scenario, in qualitative
agreement with the observed CSM morphology. Our observations require Kepler to
have originated in a close binary system with an AGB star companion.
Kepler's supernova remnant resulted from a thermonuclear explosion, but is
interacting with circumstellar material (CSM) lost from the progenitor system.
We describe a statistical technique for isolating X-ray emission due to CSM
from that due to shocked ejecta. Shocked CSM coincides well in position with 24
$\mu$m emission seen by {\sl Spitzer}. We find most CSM to be distributed along
the bright north rim, but substantial concentrations are also found projected
against the center of the remnant, roughly along a diameter with position angle
$\sim 100^\circ$. We interpret this as evidence for a disk distribution of CSM
before the SN, with the line of sight to the observer roughly in the disk
plane. We present 2-D hydrodynamic simulations of this scenario, in qualitative
agreement with the observed CSM morphology. Our observations require Kepler to
have originated in a close binary system with an AGB star companion.
Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results. (arXiv:1212.5226v1 [astro-ph.CO])
Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results. (arXiv:1212.5226v1 [astro-ph.CO]):
We present cosmological parameter constraints based on the final nine-year
WMAP data, in conjunction with additional cosmological data sets. The WMAP data
alone, and in combination, continue to be remarkably well fit by a
six-parameter LCDM model. When WMAP data are combined with measurements of the
high-l CMB anisotropy, the BAO scale, and the Hubble constant, the densities,
Omegabh2, Omegach2, and Omega_L, are each determined to a precision of ~1.5%.
The amplitude of the primordial spectrum is measured to within 3%, and there is
now evidence for a tilt in the primordial spectrum at the 5sigma level,
confirming the first detection of tilt based on the five-year WMAP data. At the
end of the WMAP mission, the nine-year data decrease the allowable volume of
the six-dimensional LCDM parameter space by a factor of 68,000 relative to
pre-WMAP measurements. We investigate a number of data combinations and show
that their LCDM parameter fits are consistent. New limits on deviations from
the six-parameter model are presented, for example: the fractional contribution
of tensor modes is limited to r<0.13 (95% CL); the spatial curvature parameter
is limited to -0.0027 (+0.0039/-0.0038); the summed mass of neutrinos is <0.44
eV (95% CL); and the number of relativistic species is found to be 3.26+/-0.35
when the full data are analyzed. The joint constraint on Neff and the
primordial helium abundance agrees with the prediction of standard Big Bang
nucleosynthesis. We compare recent PLANCK measurements of the
Sunyaev-Zel'dovich effect with our seven-year measurements, and show their
mutual agreement. Our analysis of the polarization pattern around temperature
extrema is updated. This confirms a fundamental prediction of the standard
cosmological model and provides a striking illustration of acoustic
oscillations and adiabatic initial conditions in the early universe.
We present cosmological parameter constraints based on the final nine-year
WMAP data, in conjunction with additional cosmological data sets. The WMAP data
alone, and in combination, continue to be remarkably well fit by a
six-parameter LCDM model. When WMAP data are combined with measurements of the
high-l CMB anisotropy, the BAO scale, and the Hubble constant, the densities,
Omegabh2, Omegach2, and Omega_L, are each determined to a precision of ~1.5%.
The amplitude of the primordial spectrum is measured to within 3%, and there is
now evidence for a tilt in the primordial spectrum at the 5sigma level,
confirming the first detection of tilt based on the five-year WMAP data. At the
end of the WMAP mission, the nine-year data decrease the allowable volume of
the six-dimensional LCDM parameter space by a factor of 68,000 relative to
pre-WMAP measurements. We investigate a number of data combinations and show
that their LCDM parameter fits are consistent. New limits on deviations from
the six-parameter model are presented, for example: the fractional contribution
of tensor modes is limited to r<0.13 (95% CL); the spatial curvature parameter
is limited to -0.0027 (+0.0039/-0.0038); the summed mass of neutrinos is <0.44
eV (95% CL); and the number of relativistic species is found to be 3.26+/-0.35
when the full data are analyzed. The joint constraint on Neff and the
primordial helium abundance agrees with the prediction of standard Big Bang
nucleosynthesis. We compare recent PLANCK measurements of the
Sunyaev-Zel'dovich effect with our seven-year measurements, and show their
mutual agreement. Our analysis of the polarization pattern around temperature
extrema is updated. This confirms a fundamental prediction of the standard
cosmological model and provides a striking illustration of acoustic
oscillations and adiabatic initial conditions in the early universe.
Measuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts. (arXiv:1212.5076v1 [astro-ph.CO])
Measuring the Dark Matter Halo Mass of X-ray AGN at z~1 using photometric redshifts. (arXiv:1212.5076v1 [astro-ph.CO]):
Data from the AEGIS, COSMOS and ECDFS surveys are combined to infer the bias
and dark matter halo mass of moderate luminosity [LX(2-10 keV) = 42.9 erg s-1]
X-ray AGN at z~1 via their cross-correlation function with galaxies. In
contrast to standard cross-correlation function estimators, we present a method
that requires spectroscopy only for the AGN and uses photometric redshift
probability distribution functions for galaxies to determine the projected
real-space AGN/galaxy cross-correlation function. The estimated dark matter
halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is
~13h-1M_solar, in agreement with previous studies at similar redshift and
luminosity ranges. Removing from the sample the 5 per cent of the AGN
associated with X-ray selected groups results in a reduction by about 0.5 dex
in the inferred AGN dark matter halo mass. The distribution of AGN in dark
matter halo mass is therefore skewed and the bulk of the population lives in
moderate mass haloes. This result favour cold gas accretion as the main channel
of supermassive black hole growth for most X-ray AGN.
Data from the AEGIS, COSMOS and ECDFS surveys are combined to infer the bias
and dark matter halo mass of moderate luminosity [LX(2-10 keV) = 42.9 erg s-1]
X-ray AGN at z~1 via their cross-correlation function with galaxies. In
contrast to standard cross-correlation function estimators, we present a method
that requires spectroscopy only for the AGN and uses photometric redshift
probability distribution functions for galaxies to determine the projected
real-space AGN/galaxy cross-correlation function. The estimated dark matter
halo mass of X-ray AGN in the combined AEGIS, COSMOS and ECDFS fields is
~13h-1M_solar, in agreement with previous studies at similar redshift and
luminosity ranges. Removing from the sample the 5 per cent of the AGN
associated with X-ray selected groups results in a reduction by about 0.5 dex
in the inferred AGN dark matter halo mass. The distribution of AGN in dark
matter halo mass is therefore skewed and the bulk of the population lives in
moderate mass haloes. This result favour cold gas accretion as the main channel
of supermassive black hole growth for most X-ray AGN.
Late Spectral Evolution of the Ejecta and Reverse Shock in SN1987A. (arXiv:1212.5052v1 [astro-ph.HE])
Late Spectral Evolution of the Ejecta and Reverse Shock in SN1987A. (arXiv:1212.5052v1 [astro-ph.HE]):
We present observations with VLT and HST of the broad emission lines from the
inner ejecta and reverse shock of SN 1987A from 1999 until 2012 (days 4381 --
9100 after explosion). We detect broad lines from H-alpha, H-beta, Mg I], Na I,
[O I], [Ca II] and a feature at 9220 A. We identify the latter line with Mg II
9218, 9244,most likely pumped by Ly-alpha fluorescence. H-alpha, and H-beta
both have a centrally peaked component, extending to 4500 km/s and a very broad
component extending to 11,000 km/s, while the other lines have only the central
component. The low velocity component comes from unshocked ejecta, heated
mainly by X-rays from the circumstellar ring collision, whereas the broad
component comes from faster ejecta passing through the reverse shock. The
reverse shock flux in H-alpha has increased by a factor of 4-6 from 2000 to
2007. After that there is a tendency of flattening of the light curve, similar
to what may be seen in soft X-rays and in the optical lines from the shocked
ring. The core component seen in H-alpha, [Ca II] and Mg II has experienced a
similar increase, consistent with that found from HST photometry. The ring-like
morphology of the ejecta is explained as a result of the X-ray illumination,
depositing energy outside of the core of the ejecta. The energy deposition in
the ejecta of the external X-rays illumination is calculated using explosion
models for SN 1987A and we predict that the outer parts of the unshocked ejecta
will continue to brighten because of this. We finally discuss evidence for dust
in the ejecta from line asymmetries.
We present observations with VLT and HST of the broad emission lines from the
inner ejecta and reverse shock of SN 1987A from 1999 until 2012 (days 4381 --
9100 after explosion). We detect broad lines from H-alpha, H-beta, Mg I], Na I,
[O I], [Ca II] and a feature at 9220 A. We identify the latter line with Mg II
9218, 9244,most likely pumped by Ly-alpha fluorescence. H-alpha, and H-beta
both have a centrally peaked component, extending to 4500 km/s and a very broad
component extending to 11,000 km/s, while the other lines have only the central
component. The low velocity component comes from unshocked ejecta, heated
mainly by X-rays from the circumstellar ring collision, whereas the broad
component comes from faster ejecta passing through the reverse shock. The
reverse shock flux in H-alpha has increased by a factor of 4-6 from 2000 to
2007. After that there is a tendency of flattening of the light curve, similar
to what may be seen in soft X-rays and in the optical lines from the shocked
ring. The core component seen in H-alpha, [Ca II] and Mg II has experienced a
similar increase, consistent with that found from HST photometry. The ring-like
morphology of the ejecta is explained as a result of the X-ray illumination,
depositing energy outside of the core of the ejecta. The energy deposition in
the ejecta of the external X-rays illumination is calculated using explosion
models for SN 1987A and we predict that the outer parts of the unshocked ejecta
will continue to brighten because of this. We finally discuss evidence for dust
in the ejecta from line asymmetries.
Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers. (arXiv:1212.4851v1 [astro-ph.HE])
Unification of X-ray winds in Seyfert galaxies: from ultra-fast outflows to warm absorbers. (arXiv:1212.4851v1 [astro-ph.HE]):
The existence of ionized X-ray absorbing layers of gas along the line of
sight to the nuclei of Seyfert galaxies is a well established observational
fact. This material is systematically outflowing and shows a large range in
parameters. However, its actual nature and dynamics are still not clear. In
order to gain insights into these important issues we performed a literature
search for papers reporting the parameters of the soft X-ray warm absorbers
(WAs) in 35 type 1 Seyferts and compared their properties to those of the
ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources
with WAs is >60%, consistent with previous studies. The fraction of sources
with UFOs is >34%, >67% of which also show WAs. The large dynamic range
obtained when considering all the absorbers together allows us, for the first
time, to investigate general relations among them. In particular, we find
significant correlations indicating that the closer the absorber is to the
central black hole, the higher the ionization, column, outflow velocity and
consequently the mechanical power. The absorbers continuously populate the
whole parameter space, with the WAs and the UFOs lying always at the two ends
of the distribution. This strongly suggest that these absorbers, often
considered of different types, could actually represent parts of a single
large-scale stratified outflow observed at different locations from the black
hole. The observed parameters and correlations are consistent with both
radiation pressure through Compton scattering and MHD processes contributing to
the outflow acceleration, the latter playing a major role. Most of the
absorbers, especially the UFOs, have a sufficiently high mechanical power to
significantly contribute to AGN feedback.
The existence of ionized X-ray absorbing layers of gas along the line of
sight to the nuclei of Seyfert galaxies is a well established observational
fact. This material is systematically outflowing and shows a large range in
parameters. However, its actual nature and dynamics are still not clear. In
order to gain insights into these important issues we performed a literature
search for papers reporting the parameters of the soft X-ray warm absorbers
(WAs) in 35 type 1 Seyferts and compared their properties to those of the
ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources
with WAs is >60%, consistent with previous studies. The fraction of sources
with UFOs is >34%, >67% of which also show WAs. The large dynamic range
obtained when considering all the absorbers together allows us, for the first
time, to investigate general relations among them. In particular, we find
significant correlations indicating that the closer the absorber is to the
central black hole, the higher the ionization, column, outflow velocity and
consequently the mechanical power. The absorbers continuously populate the
whole parameter space, with the WAs and the UFOs lying always at the two ends
of the distribution. This strongly suggest that these absorbers, often
considered of different types, could actually represent parts of a single
large-scale stratified outflow observed at different locations from the black
hole. The observed parameters and correlations are consistent with both
radiation pressure through Compton scattering and MHD processes contributing to
the outflow acceleration, the latter playing a major role. Most of the
absorbers, especially the UFOs, have a sufficiently high mechanical power to
significantly contribute to AGN feedback.
Wednesday, December 19, 2012
Planck Intermediate Results. XI: The gas content of dark matter halos: the Sunyaev-Zeldovich-stellar mass relation for locally brightest galaxies. (arXiv:1212.4131v1 [astro-ph.CO])
Planck Intermediate Results. XI: The gas content of dark matter halos: the Sunyaev-Zeldovich-stellar mass relation for locally brightest galaxies. (arXiv:1212.4131v1 [astro-ph.CO]):
We present the scaling relation between Sunyaev-Zeldovich (SZ) signal and
stellar mass for almost 260,000 locally brightest galaxies (LBGs) selected from
the Sloan Digital Sky Survey (SDSS). These are predominantly the central
galaxies of their dark matter halos. We calibrate the stellar-to-halo mass
conversion using realistic mock catalogues based on the Millennium Simulation.
Applying a multi-frequency matched filter to the Planck data for each LBG, and
averaging the results in bins of stellar mass, we measure the mean SZ signal
down to $M_\ast\sim 2\times 10^{11} \Msolar$, with a clear indication of signal
at even lower stellar mass. We derive the scaling relation between SZ signal
and halo mass by assigning halo properties from our mock catalogues to the real
LBGs and simulating the Planck observation process. This relation shows no
evidence for deviation from a power law over a halo mass range extending from
rich clusters down to $M_{500}\sim 2\times 10^{13} \Msolar$, and there is a
clear indication of signal down to $M_{500}\sim 4\times 10^{12} \Msolar$.
Planck's SZ detections in such low-mass halos imply that about a quarter of all
baryons have now been seen in the form of hot halo gas, and that this gas must
be less concentrated than the dark matter in such halos in order to remain
consistent with X-ray observations. At the high-mass end, the measured SZ
signal is 20% lower than found from observations of X-ray clusters, a
difference consistent with Malmquist bias effects in the X-ray sample.
We present the scaling relation between Sunyaev-Zeldovich (SZ) signal and
stellar mass for almost 260,000 locally brightest galaxies (LBGs) selected from
the Sloan Digital Sky Survey (SDSS). These are predominantly the central
galaxies of their dark matter halos. We calibrate the stellar-to-halo mass
conversion using realistic mock catalogues based on the Millennium Simulation.
Applying a multi-frequency matched filter to the Planck data for each LBG, and
averaging the results in bins of stellar mass, we measure the mean SZ signal
down to $M_\ast\sim 2\times 10^{11} \Msolar$, with a clear indication of signal
at even lower stellar mass. We derive the scaling relation between SZ signal
and halo mass by assigning halo properties from our mock catalogues to the real
LBGs and simulating the Planck observation process. This relation shows no
evidence for deviation from a power law over a halo mass range extending from
rich clusters down to $M_{500}\sim 2\times 10^{13} \Msolar$, and there is a
clear indication of signal down to $M_{500}\sim 4\times 10^{12} \Msolar$.
Planck's SZ detections in such low-mass halos imply that about a quarter of all
baryons have now been seen in the form of hot halo gas, and that this gas must
be less concentrated than the dark matter in such halos in order to remain
consistent with X-ray observations. At the high-mass end, the measured SZ
signal is 20% lower than found from observations of X-ray clusters, a
difference consistent with Malmquist bias effects in the X-ray sample.
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO])
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO]):
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
The Escape Fraction of Ionizing Radiation from Primordial Galaxies. (arXiv:1212.4452v1 [astro-ph.CO])
The Escape Fraction of Ionizing Radiation from Primordial Galaxies. (arXiv:1212.4452v1 [astro-ph.CO]):
The escape of ionizing radiation from galaxies plays a critical role in the
evolution of gas in galaxies, and the heating and ionization history of the
intergalactic medium. Here, we present semi-analytic calculations of the escape
fraction of ionizing radiation for both hydrogen and helium from primordial
galaxies, as well as analytic derivations of these quantities. We consider
variations in the galaxy density profile, source type, location, and spectrum,
and gas clumping/distribution factors. For sufficiently hard first-light
sources, the helium ionization fronts closely track or even advance beyond that
of hydrogen. Key new results in this work include calculations of the escape
fractions for He I and He II ionizing radiation, and the impact of partial
ionization from X-rays from early AGN or stellar clusters on the escape
fractions from primordial halos. When factoring in frequency-dependent effects,
we find that X-rays play an important role in boosting the escape fractions for
both hydrogen and helium, but especially for He II. We briefly discuss the
implications of these results for recent observations of the He II reionization
epoch at low redshifts, as well as the UV data and emission-line signatures
from early galaxies anticipated from future satellite missions.
The escape of ionizing radiation from galaxies plays a critical role in the
evolution of gas in galaxies, and the heating and ionization history of the
intergalactic medium. Here, we present semi-analytic calculations of the escape
fraction of ionizing radiation for both hydrogen and helium from primordial
galaxies, as well as analytic derivations of these quantities. We consider
variations in the galaxy density profile, source type, location, and spectrum,
and gas clumping/distribution factors. For sufficiently hard first-light
sources, the helium ionization fronts closely track or even advance beyond that
of hydrogen. Key new results in this work include calculations of the escape
fractions for He I and He II ionizing radiation, and the impact of partial
ionization from X-rays from early AGN or stellar clusters on the escape
fractions from primordial halos. When factoring in frequency-dependent effects,
we find that X-rays play an important role in boosting the escape fractions for
both hydrogen and helium, but especially for He II. We briefly discuss the
implications of these results for recent observations of the He II reionization
epoch at low redshifts, as well as the UV data and emission-line signatures
from early galaxies anticipated from future satellite missions.
Thin-shell mixing in radiative wind-shocks and the Lx-Lbol scaling of O-star X-rays. (arXiv:1212.4235v1 [astro-ph.SR])
Thin-shell mixing in radiative wind-shocks and the Lx-Lbol scaling of O-star X-rays. (arXiv:1212.4235v1 [astro-ph.SR]):
X-ray satellites since Einstein have empirically established that the X-ray
luminosity from single O-stars scales linearly with bolometric luminosity, Lx ~
10^{-7} Lbol. But straightforward forms of the most favored model, in which
X-rays arise from instability-generated shocks embedded in the stellar wind,
predict a steeper scaling, either with mass loss rate Lx ~ Mdot ~ Lbol^{1.7} if
the shocks are radiative, or with Lx ~ Mdot^{2} ~ Lbol^{3.4} if they are
adiabatic. This paper presents a generalized formalism that bridges these
radiative vs. adiabatic limits in terms of the ratio of the shock cooling
length to the local radius. Noting that the thin-shell instability of radiative
shocks should lead to extensive mixing of hot and cool material, we propose
that the associated softening and weakening of the X-ray emission can be
parametrized as scaling with the cooling length ratio raised to a power m$, the
"mixing exponent". For physically reasonable values m ~= 0.4, this leads to an
X-ray luminosity Lx ~ Mdot^{0.6} ~ Lbol that matches the empirical scaling. To
fit observed X-ray line profiles, we find such radiative-shock-mixing models
require the number of shocks to drop sharply above the initial shock onset
radius. This in turn implies that the X-ray luminosity should saturate and even
decrease for optically thick winds with very high mass-loss rates. In the
opposite limit of adiabatic shocks in low-density winds (e.g., from B-stars),
the X-ray luminosity should drop steeply with Mdot^2. Future numerical
simulation studies will be needed to test the general thin-shell mixing ansatz
for X-ray emission.
X-ray satellites since Einstein have empirically established that the X-ray
luminosity from single O-stars scales linearly with bolometric luminosity, Lx ~
10^{-7} Lbol. But straightforward forms of the most favored model, in which
X-rays arise from instability-generated shocks embedded in the stellar wind,
predict a steeper scaling, either with mass loss rate Lx ~ Mdot ~ Lbol^{1.7} if
the shocks are radiative, or with Lx ~ Mdot^{2} ~ Lbol^{3.4} if they are
adiabatic. This paper presents a generalized formalism that bridges these
radiative vs. adiabatic limits in terms of the ratio of the shock cooling
length to the local radius. Noting that the thin-shell instability of radiative
shocks should lead to extensive mixing of hot and cool material, we propose
that the associated softening and weakening of the X-ray emission can be
parametrized as scaling with the cooling length ratio raised to a power m$, the
"mixing exponent". For physically reasonable values m ~= 0.4, this leads to an
X-ray luminosity Lx ~ Mdot^{0.6} ~ Lbol that matches the empirical scaling. To
fit observed X-ray line profiles, we find such radiative-shock-mixing models
require the number of shocks to drop sharply above the initial shock onset
radius. This in turn implies that the X-ray luminosity should saturate and even
decrease for optically thick winds with very high mass-loss rates. In the
opposite limit of adiabatic shocks in low-density winds (e.g., from B-stars),
the X-ray luminosity should drop steeply with Mdot^2. Future numerical
simulation studies will be needed to test the general thin-shell mixing ansatz
for X-ray emission.
The X-ray-Optical Relations for Nine Clusters at z = 0.7-1.1. (arXiv:1212.4219v1 [astro-ph.CO])
The X-ray-Optical Relations for Nine Clusters at z = 0.7-1.1. (arXiv:1212.4219v1 [astro-ph.CO]):
We use Chandra observations of nine optically and X-ray selected clusters in
five different structures at z ~ 0.7-1.1 from the Observations of Redshift
Evolution in Large-Scale Environments (ORELSE) survey to study diffuse X-ray
emission from galaxy clusters. X-ray gas temperatures and bolometric rest-frame
luminosities are measured for each cluster in the sample. We present new
redshift measurements, derived from dataobtained using the Deep Imaging
Multi-Object Spectrograph on the Keck 10-m telescope, for two clusters in the
RX J0910 supercluster at z ~ 1.1, from which velocity dispersions are measured.
Dispersions for all clusters are combined with X-ray luminosities and gas
temperatures to evaluate how the cluster properties compare to low-redshift
scaling relations. We also measure the degree of substructure in each cluster
by examining the velocity histograms, performing Dressler-Shectman tests, and
computing the offsets between the X-ray emission center and optically-derived
centroids. We find that only two clusters show clear indications of being
unrelaxed, based on their scaling relations and other dynamical state
diagnostics. Using our sample, we evaluate the redshift evolution of the L_x-T
relation and investigate the implications of our results for precision
cosmology surveys.
We use Chandra observations of nine optically and X-ray selected clusters in
five different structures at z ~ 0.7-1.1 from the Observations of Redshift
Evolution in Large-Scale Environments (ORELSE) survey to study diffuse X-ray
emission from galaxy clusters. X-ray gas temperatures and bolometric rest-frame
luminosities are measured for each cluster in the sample. We present new
redshift measurements, derived from dataobtained using the Deep Imaging
Multi-Object Spectrograph on the Keck 10-m telescope, for two clusters in the
RX J0910 supercluster at z ~ 1.1, from which velocity dispersions are measured.
Dispersions for all clusters are combined with X-ray luminosities and gas
temperatures to evaluate how the cluster properties compare to low-redshift
scaling relations. We also measure the degree of substructure in each cluster
by examining the velocity histograms, performing Dressler-Shectman tests, and
computing the offsets between the X-ray emission center and optically-derived
centroids. We find that only two clusters show clear indications of being
unrelaxed, based on their scaling relations and other dynamical state
diagnostics. Using our sample, we evaluate the redshift evolution of the L_x-T
relation and investigate the implications of our results for precision
cosmology surveys.
Quark-hybrid matter in the cores of massive neutron stars. (arXiv:1212.4213v1 [astro-ph.SR])
Quark-hybrid matter in the cores of massive neutron stars. (arXiv:1212.4213v1 [astro-ph.SR]):
Using a nonlocal extension of the SU(3) Nambu-Jona Lasinio model, which
reproduces several of the key features of Quantum Chromodynamics, we show that
mixed phases of deconfined quarks and confined hadrons (quark-hybrid matter)
may exist in the cores of neutron stars as massive as around 2.1 M_Sun. The
radii of these objects are found to be in the canonical range of $\sim 12-13$
km. According to our study, the transition to pure quark matter does not occur
in stable neutron stars, but is shifted to neutron stars which are unstable
against radial oscillations. The implications of our study for the recently
discovered, massive neutron star PSR J1614-2230, whose gravitational mass is
$1.97 \pm 0.04 M_Sun$, are that this neutron star may contain an extended
region of quark-hybrid matter at it center, but no pure quark matter.
Using a nonlocal extension of the SU(3) Nambu-Jona Lasinio model, which
reproduces several of the key features of Quantum Chromodynamics, we show that
mixed phases of deconfined quarks and confined hadrons (quark-hybrid matter)
may exist in the cores of neutron stars as massive as around 2.1 M_Sun. The
radii of these objects are found to be in the canonical range of $\sim 12-13$
km. According to our study, the transition to pure quark matter does not occur
in stable neutron stars, but is shifted to neutron stars which are unstable
against radial oscillations. The implications of our study for the recently
discovered, massive neutron star PSR J1614-2230, whose gravitational mass is
$1.97 \pm 0.04 M_Sun$, are that this neutron star may contain an extended
region of quark-hybrid matter at it center, but no pure quark matter.
Distant galaxy clusters in the XMM Large Scale Structure survey. (arXiv:1212.4185v1 [astro-ph.CO])
Distant galaxy clusters in the XMM Large Scale Structure survey. (arXiv:1212.4185v1 [astro-ph.CO]):
(Abridged) Distant galaxy clusters provide important tests of the growth of
large scale structure in addition to highlighting the process of galaxy
evolution in a consistently defined environment at large look back time. We
present a sample of 22 distant (z>0.8) galaxy clusters and cluster candidates
selected from the 9 deg2 footprint of the overlapping X-ray Multi Mirror (XMM)
Large Scale Structure (LSS), CFHTLS Wide and Spitzer SWIRE surveys. Clusters
are selected as extended X-ray sources with an accompanying overdensity of
galaxies displaying optical to mid-infrared photometry consistent with z>0.8.
Nine clusters have confirmed spectroscopic redshifts in the interval 0.8<z<1.2,
four of which are presented here for the first time. A further 11 candidate
clusters have between 8 and 10 band photometric redshifts in the interval
0.8<z<2.2, while the remaining two candidates do not have information in
sufficient wavebands to generate a reliable photometric redshift. All of the
candidate clusters reported in this paper are presented for the first time.
Those confirmed and candidate clusters with available near infrared photometry
display evidence for a red sequence galaxy population, determined either
individually or via a stacking analysis, whose colour is consistent with the
expectation of an old, coeval stellar population observed at the cluster
redshift. We further note that the sample displays a large range of red
fraction values indicating that the clusters may be at different stages of red
sequence assembly. We compare the observed X-ray emission to the flux expected
from a suite of model clusters and find that the sample displays an effective
mass limit M200 ~ 1e14 Msolar with all clusters displaying masses consistent
with M200 < 5e14 Msolar. This XMM distant cluster study represents a complete
sample of X-ray selected z>0.8 clusters.
(Abridged) Distant galaxy clusters provide important tests of the growth of
large scale structure in addition to highlighting the process of galaxy
evolution in a consistently defined environment at large look back time. We
present a sample of 22 distant (z>0.8) galaxy clusters and cluster candidates
selected from the 9 deg2 footprint of the overlapping X-ray Multi Mirror (XMM)
Large Scale Structure (LSS), CFHTLS Wide and Spitzer SWIRE surveys. Clusters
are selected as extended X-ray sources with an accompanying overdensity of
galaxies displaying optical to mid-infrared photometry consistent with z>0.8.
Nine clusters have confirmed spectroscopic redshifts in the interval 0.8<z<1.2,
four of which are presented here for the first time. A further 11 candidate
clusters have between 8 and 10 band photometric redshifts in the interval
0.8<z<2.2, while the remaining two candidates do not have information in
sufficient wavebands to generate a reliable photometric redshift. All of the
candidate clusters reported in this paper are presented for the first time.
Those confirmed and candidate clusters with available near infrared photometry
display evidence for a red sequence galaxy population, determined either
individually or via a stacking analysis, whose colour is consistent with the
expectation of an old, coeval stellar population observed at the cluster
redshift. We further note that the sample displays a large range of red
fraction values indicating that the clusters may be at different stages of red
sequence assembly. We compare the observed X-ray emission to the flux expected
from a suite of model clusters and find that the sample displays an effective
mass limit M200 ~ 1e14 Msolar with all clusters displaying masses consistent
with M200 < 5e14 Msolar. This XMM distant cluster study represents a complete
sample of X-ray selected z>0.8 clusters.
Constraining the Accretion Flow in Sgr A* by General Relativistic Dynamical and Polarized Radiative Modeling. (arXiv:1212.4149v1 [astro-ph.HE])
Constraining the Accretion Flow in Sgr A* by General Relativistic Dynamical and Polarized Radiative Modeling. (arXiv:1212.4149v1 [astro-ph.HE]):
We briefly summarize the method of simulating Sgr A* polarized sub-mm spectra
from the accretion flow and fitting the observed spectrum. The dynamical flow
model is based on three-dimensional general relativistic magneto hydrodynamic
simulations. Fully self-consistent radiative transfer of polarized
cyclo-synchrotron emission is performed. We compile a mean sub-mm spectrum of
Sgr A* and fit it with the mean simulated spectra. We estimate the ranges of
inclination angle theta=42-75deg, mass accretion rate
Mdot=(1.4-7.0)*10^{-8}Msun/yr, and electron temperature Te=(3-4)*10^{10}K at
6M. We discuss multiple caveats in dynamical modeling, which must be resolved
to make further progress.
We briefly summarize the method of simulating Sgr A* polarized sub-mm spectra
from the accretion flow and fitting the observed spectrum. The dynamical flow
model is based on three-dimensional general relativistic magneto hydrodynamic
simulations. Fully self-consistent radiative transfer of polarized
cyclo-synchrotron emission is performed. We compile a mean sub-mm spectrum of
Sgr A* and fit it with the mean simulated spectra. We estimate the ranges of
inclination angle theta=42-75deg, mass accretion rate
Mdot=(1.4-7.0)*10^{-8}Msun/yr, and electron temperature Te=(3-4)*10^{10}K at
6M. We discuss multiple caveats in dynamical modeling, which must be resolved
to make further progress.
Monday, December 17, 2012
Density Profile of Cool Core of Galaxy Clusters. (arXiv:1212.0671v1 [astro-ph.CO])
Density Profile of Cool Core of Galaxy Clusters. (arXiv:1212.0671v1 [astro-ph.CO]):
The density profile of cool core of intracluster gas is investigated, for a
cluster of galaxies that is initially in the virial equilibrium state and then
undergoes radiative cooling. The initial gas profile is derived under the
assumption that the gas is hydrostatic within the dark matter potential
presented by so-called NFW or King model and has a polytropic profile. The
contribution from masses of gas and galaxies to the potential is ignored
compared to the dark matter in the calculation. The temperature and density
profiles of gas in its quasi-hydrostatic cooling phase, which is expected to
last for ~Gyr, is then calculated for different initial gas profiles. It is
found that in the quasi-hydrostatic cooling phase, while the temperature
decreases to be about one-third, the density increases by a factor of 4-6 at
the cluster center in comparison with their initial polytropic values, though
the profiles over the core depend on the dark matter potential. Hence, the core
radius in the quasi hydrostatic cooling gas appears smaller than the initial
polytropic one. We compare the density profile of the cool core with
observations to find that while the initial density is around the upper bounds
of large-core (>100 kpc) clusters, likely most relaxed but cooling is not yet
significant, the central density under quasi-hydrostatic cooling falls between
the mid- and high-values of small-core (<100 kpc) or cool-core clusters. It is
also found for the quasi-hydrostatic cooling gas that the entropy profile
roughly agrees with the best-fit model for the ACCEPT cluster sample with a low
central entropy, and the pressure gradient in the inner core is close to that
of the REXCESS sample. X-ray surface brightness calculated for the
quasi-hydrostatic cooling gas is well represented by the conventional double
beta-model, giving a physical basis of applying the double beta-model to cool
core clusters.
The density profile of cool core of intracluster gas is investigated, for a
cluster of galaxies that is initially in the virial equilibrium state and then
undergoes radiative cooling. The initial gas profile is derived under the
assumption that the gas is hydrostatic within the dark matter potential
presented by so-called NFW or King model and has a polytropic profile. The
contribution from masses of gas and galaxies to the potential is ignored
compared to the dark matter in the calculation. The temperature and density
profiles of gas in its quasi-hydrostatic cooling phase, which is expected to
last for ~Gyr, is then calculated for different initial gas profiles. It is
found that in the quasi-hydrostatic cooling phase, while the temperature
decreases to be about one-third, the density increases by a factor of 4-6 at
the cluster center in comparison with their initial polytropic values, though
the profiles over the core depend on the dark matter potential. Hence, the core
radius in the quasi hydrostatic cooling gas appears smaller than the initial
polytropic one. We compare the density profile of the cool core with
observations to find that while the initial density is around the upper bounds
of large-core (>100 kpc) clusters, likely most relaxed but cooling is not yet
significant, the central density under quasi-hydrostatic cooling falls between
the mid- and high-values of small-core (<100 kpc) or cool-core clusters. It is
also found for the quasi-hydrostatic cooling gas that the entropy profile
roughly agrees with the best-fit model for the ACCEPT cluster sample with a low
central entropy, and the pressure gradient in the inner core is close to that
of the REXCESS sample. X-ray surface brightness calculated for the
quasi-hydrostatic cooling gas is well represented by the conventional double
beta-model, giving a physical basis of applying the double beta-model to cool
core clusters.
The COS-Halos Survey: An Empirical Description of the Metal-Line Absorption in the Low-Redshift Circumgalactic Medium. (arXiv:1212.0558v1 [astro-ph.CO])
The COS-Halos Survey: An Empirical Description of the Metal-Line Absorption in the Low-Redshift Circumgalactic Medium. (arXiv:1212.0558v1 [astro-ph.CO]):
We present the equivalent width and column density measurements for low and
intermediate ionization states of the circumgalactic medium (CGM) surrounding
44 low-z, L ~ L* galaxies drawn from the COS-Halos survey. These measurements
are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra
of background quasars within an impact parameter R < 160 kpc to the targeted
galaxies. The data show significant metal-line absorption for 33 of the 44
galaxies, including quiescent systems, revealing the common occurance of a cool
(T ~ 10^{4 - 5} K), metal-enriched CGM. The detection rates and column
densities derived for these metal lines decrease with increasing impact
parameter, a trend we interpret as a declining metal surface density profile
for the CGM. A comparison of the relative column densities of adjacent
ionization states indicates the gas is predominantly ionized. The large surface
density in metals demands a large reservoir of metals and gas in the cool CGM
(very conservatively, M_ CGMcool > 10^9 MSun), which likely traces a distinct
density and/or temperature regime from the highly-ionized CGM traced by OVI
absorption. The large dispersion in absorption strengths (including
non-detections) suggests the cool CGM traces a wide range of densities or a mix
of local ionizing conditions. Lastly, the kinematics inferred from the
metal-line profiles are consistent with the cool CGM being bound to the dark
matters halos hosting the galaxies; this gas may serve as fuel for future
star-formation. Future work will leverage this dataset to provide estimates on
the mass, metallicity, dynamics, and origin of the cool CGM in low-z, L*
galaxies.
We present the equivalent width and column density measurements for low and
intermediate ionization states of the circumgalactic medium (CGM) surrounding
44 low-z, L ~ L* galaxies drawn from the COS-Halos survey. These measurements
are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra
of background quasars within an impact parameter R < 160 kpc to the targeted
galaxies. The data show significant metal-line absorption for 33 of the 44
galaxies, including quiescent systems, revealing the common occurance of a cool
(T ~ 10^{4 - 5} K), metal-enriched CGM. The detection rates and column
densities derived for these metal lines decrease with increasing impact
parameter, a trend we interpret as a declining metal surface density profile
for the CGM. A comparison of the relative column densities of adjacent
ionization states indicates the gas is predominantly ionized. The large surface
density in metals demands a large reservoir of metals and gas in the cool CGM
(very conservatively, M_ CGMcool > 10^9 MSun), which likely traces a distinct
density and/or temperature regime from the highly-ionized CGM traced by OVI
absorption. The large dispersion in absorption strengths (including
non-detections) suggests the cool CGM traces a wide range of densities or a mix
of local ionizing conditions. Lastly, the kinematics inferred from the
metal-line profiles are consistent with the cool CGM being bound to the dark
matters halos hosting the galaxies; this gas may serve as fuel for future
star-formation. Future work will leverage this dataset to provide estimates on
the mass, metallicity, dynamics, and origin of the cool CGM in low-z, L*
galaxies.
What Sets Temperature Gradients in Galaxy Clusters? Implications for non-thermal pressure support and mass-observable scaling relations. (arXiv:1212.0543v1 [astro-ph.CO])
What Sets Temperature Gradients in Galaxy Clusters? Implications for non-thermal pressure support and mass-observable scaling relations. (arXiv:1212.0543v1 [astro-ph.CO]):
We present a spherically symmetric model for the origin and evolution of the
temperature profiles in the hot plasma filling galaxy groups and clusters. We
find that the gas in clusters is generically not isothermal, and that the
temperature declines with radius at large distances from the cluster center
(outside the core- and scale radii). This temperature profile is determined by
the accretion history of the halo, and is not quantitatively well-described by
a polytropic model. We explain quantitatively how the large-scale temperature
gradient persists in spite of thermal conduction and convection. These results
are a consequence of the cosmological assembly of clusters and cannot be
reproduced with non-cosmological simulations of isolated halos. We show that
the variation in halo assembly histories produces a ~10% scatter in temperature
at fixed mass. On top of this scatter, conduction decreases the temperature of
the gas near the scale radius in massive clusters, which may bias hydrostatic
mass estimates inferred from x-ray and SZ observations. As an example
application of our model profiles, we use mixing-length theory to estimate the
turbulent pressure support created by the magnetothermal instability (MTI): in
agreement with our earlier MHD simulations, we find that the convection
produced by the MTI can provide ~5% non-thermal pressure support near r_500.
The magnitude of this turbulent pressure support is likely to be non-monotonic
in halo mass, peaking in ~10^14.5 M_sun halos.
We present a spherically symmetric model for the origin and evolution of the
temperature profiles in the hot plasma filling galaxy groups and clusters. We
find that the gas in clusters is generically not isothermal, and that the
temperature declines with radius at large distances from the cluster center
(outside the core- and scale radii). This temperature profile is determined by
the accretion history of the halo, and is not quantitatively well-described by
a polytropic model. We explain quantitatively how the large-scale temperature
gradient persists in spite of thermal conduction and convection. These results
are a consequence of the cosmological assembly of clusters and cannot be
reproduced with non-cosmological simulations of isolated halos. We show that
the variation in halo assembly histories produces a ~10% scatter in temperature
at fixed mass. On top of this scatter, conduction decreases the temperature of
the gas near the scale radius in massive clusters, which may bias hydrostatic
mass estimates inferred from x-ray and SZ observations. As an example
application of our model profiles, we use mixing-length theory to estimate the
turbulent pressure support created by the magnetothermal instability (MTI): in
agreement with our earlier MHD simulations, we find that the convection
produced by the MTI can provide ~5% non-thermal pressure support near r_500.
The magnitude of this turbulent pressure support is likely to be non-monotonic
in halo mass, peaking in ~10^14.5 M_sun halos.
Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO])
Hot X-ray coronae around massive spiral galaxies: a unique probe of structure formation models. (arXiv:1212.0541v1 [astro-ph.CO]):
Luminous X-ray gas coronae in the dark matter halos of massive spiral
galaxies are a fundamental prediction of structure formation models, yet such
coronae remained essentially unexplored. In this paper, for the very first
time, we detect and characterize extended hot X-ray coronae beyond the optical
disks of two normal massive spiral galaxies, NGC1961 and NGC6753. Based on
XMM-Newton X-ray observations, we detect hot gaseous emission extending out to
~60 kpc around both galaxies - well beyond their optical radii. The hot gas,
whose best-fit temperature is kT~0.6 keV and abundance is ~0.1 Solar, appears
to have a fairly uniform distribution, hinting that the quasi-static gas
resides in hydrostatic equilibrium in the potential well of the galaxies. The
bolometric luminosity of the hot gas in the (0.05-0.15)r_200 region, where
r_200 is the virial radius, is ~6e40 erg/s for both NGC1961 and NGC6753. We
derive the baryon mass fractions of NGC1961 and NGC6753 and obtain f_b~0.1,
which values fall short of the cosmic baryon fraction. The detected X-ray
coronae around NGC1961 and NGC6753 offer an excellent basis to probe structure
formation simulations. To this end, the observations are confronted with the
recently developed moving mesh code AREPO and the traditionally used smoothed
particle hydrodynamics code GADGET. The implemented subresolution physics and
the gravity solver are identical in the two codes, but they use different
methods to solve the hydrodynamical equations. We conclude that, while neither
model gives a perfect description, the observed luminosities, gas masses, and
abundances favor the AREPO code. Moreover, the shape of the observed density
profiles are also well reproduced by AREPO within ~0.4r_200. However, neither
model incorporates efficient feedback from supermassive black holes or
supernovae, which could alter the simulated properties of the X-ray coronae.
(abridged)
Luminous X-ray gas coronae in the dark matter halos of massive spiral
galaxies are a fundamental prediction of structure formation models, yet such
coronae remained essentially unexplored. In this paper, for the very first
time, we detect and characterize extended hot X-ray coronae beyond the optical
disks of two normal massive spiral galaxies, NGC1961 and NGC6753. Based on
XMM-Newton X-ray observations, we detect hot gaseous emission extending out to
~60 kpc around both galaxies - well beyond their optical radii. The hot gas,
whose best-fit temperature is kT~0.6 keV and abundance is ~0.1 Solar, appears
to have a fairly uniform distribution, hinting that the quasi-static gas
resides in hydrostatic equilibrium in the potential well of the galaxies. The
bolometric luminosity of the hot gas in the (0.05-0.15)r_200 region, where
r_200 is the virial radius, is ~6e40 erg/s for both NGC1961 and NGC6753. We
derive the baryon mass fractions of NGC1961 and NGC6753 and obtain f_b~0.1,
which values fall short of the cosmic baryon fraction. The detected X-ray
coronae around NGC1961 and NGC6753 offer an excellent basis to probe structure
formation simulations. To this end, the observations are confronted with the
recently developed moving mesh code AREPO and the traditionally used smoothed
particle hydrodynamics code GADGET. The implemented subresolution physics and
the gravity solver are identical in the two codes, but they use different
methods to solve the hydrodynamical equations. We conclude that, while neither
model gives a perfect description, the observed luminosities, gas masses, and
abundances favor the AREPO code. Moreover, the shape of the observed density
profiles are also well reproduced by AREPO within ~0.4r_200. However, neither
model incorporates efficient feedback from supermassive black holes or
supernovae, which could alter the simulated properties of the X-ray coronae.
(abridged)
The baryon budget on the galaxy group/cluster boundary. (arXiv:1212.1613v1 [astro-ph.CO])
The baryon budget on the galaxy group/cluster boundary. (arXiv:1212.1613v1 [astro-ph.CO]):
We present a study of the hot gas and stellar content of 5 optically-selected
poor galaxy clusters, including a full accounting of the contribution from
intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass
analysis with XMM observations. We find weighted mean stellar (including ICL),
gas and total baryon mass fractions within r500 of 0.026+/-0.003, 0.070+/-0.005
and 0.096+/-0.006, respectively, at a corresponding weighted mean M500 of
(1.08_{-0.18}^{+0.21}) x 10^14 Msun. Even when accounting for the intracluster
stars, 4 out of 5 clusters show evidence for a substantial baryon deficit
within r500, with baryon fractions (f_bary) between 50+/-6 to 59+/-8 per cent
of the Universal mean level (i.e. Omega_b / Omega_m); the remaining cluster
having f_bary = 75+/-11 per cent. For the 3 clusters where we can trace the hot
halo to r500 we find no evidence for a steepening of the gas density profile in
the outskirts with respect to a power law, as seen in more massive clusters. We
find that in all cases, the X-ray mass measurements are larger than those
originally published on the basis of the galaxy velocity dispersion (sigma) and
an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased
masses, the stellar fractions (in the range 0.016-0.034, within r500) remain
consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff
(2007), from which our sample is drawn.
We present a study of the hot gas and stellar content of 5 optically-selected
poor galaxy clusters, including a full accounting of the contribution from
intracluster light (ICL) and a combined hot gas and hydrostatic X-ray mass
analysis with XMM observations. We find weighted mean stellar (including ICL),
gas and total baryon mass fractions within r500 of 0.026+/-0.003, 0.070+/-0.005
and 0.096+/-0.006, respectively, at a corresponding weighted mean M500 of
(1.08_{-0.18}^{+0.21}) x 10^14 Msun. Even when accounting for the intracluster
stars, 4 out of 5 clusters show evidence for a substantial baryon deficit
within r500, with baryon fractions (f_bary) between 50+/-6 to 59+/-8 per cent
of the Universal mean level (i.e. Omega_b / Omega_m); the remaining cluster
having f_bary = 75+/-11 per cent. For the 3 clusters where we can trace the hot
halo to r500 we find no evidence for a steepening of the gas density profile in
the outskirts with respect to a power law, as seen in more massive clusters. We
find that in all cases, the X-ray mass measurements are larger than those
originally published on the basis of the galaxy velocity dispersion (sigma) and
an assumed sigma-M500 relation, by a factor of 1.7-5.7. Despite these increased
masses, the stellar fractions (in the range 0.016-0.034, within r500) remain
consistent with the trend with mass published by Gonzalez, Zaritsky & Zabludoff
(2007), from which our sample is drawn.
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) III. Construction of the first flux-limited supercluster sample. (arXiv:1212.1597v1 [astro-ph.CO])
The extended ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey (REFLEX II) III. Construction of the first flux-limited supercluster sample. (arXiv:1212.1597v1 [astro-ph.CO]):
We present the first supercluster catalogue constructed with the extended
ROSAT-ESO Flux Limited X-ray Galaxy Cluster survey (REFLEX II) data, which
comprises 919 X-ray selected galaxy clusters. Based on this cluster catalogue
we construct a supercluster catalogue using a friends-of-friends algorithm with
a linking length depending on the local cluster density. The resulting
catalogue comprises 164 superclusters at redshift z<=0.4. We study the
properties of different catalogues such as the distributions of the redshift,
extent and multiplicity by varying the choice of parameters. In addition to the
main catalogue we compile a large volume-limited cluster sample to investigate
the statistics of the superclusters. We also compare the X-ray luminosity
function for the clusters in superclusters with that for the field clusters
with the flux- and volume-limited catalogues. The results mildly support the
theoretical suggestion of a top-heavy X-ray luminosity function of galaxy
clusters in regions of high cluster density.
We present the first supercluster catalogue constructed with the extended
ROSAT-ESO Flux Limited X-ray Galaxy Cluster survey (REFLEX II) data, which
comprises 919 X-ray selected galaxy clusters. Based on this cluster catalogue
we construct a supercluster catalogue using a friends-of-friends algorithm with
a linking length depending on the local cluster density. The resulting
catalogue comprises 164 superclusters at redshift z<=0.4. We study the
properties of different catalogues such as the distributions of the redshift,
extent and multiplicity by varying the choice of parameters. In addition to the
main catalogue we compile a large volume-limited cluster sample to investigate
the statistics of the superclusters. We also compare the X-ray luminosity
function for the clusters in superclusters with that for the field clusters
with the flux- and volume-limited catalogues. The results mildly support the
theoretical suggestion of a top-heavy X-ray luminosity function of galaxy
clusters in regions of high cluster density.
A detailed X-ray investigation of zeta Puppis - The variability on short and long timescales. (arXiv:1212.1554v1 [astro-ph.SR])
A detailed X-ray investigation of zeta Puppis - The variability on short and long timescales. (arXiv:1212.1554v1 [astro-ph.SR]):
Stellar winds are a crucial component of massive stars, but their exact
properties still remain uncertain. To shed some light on this subject, we have
analyzed an exceptional set of X-ray observations of zeya Pup, one of the
closest and brightest massive stars. The sensitive lightcurves that were
derived reveal two major results. On the one hand, a slow modulation of the
X-ray flux (with a relative amplitude of up to 15% over 16h in the 0.3--4.0keV
band) is detected. Its characteristic timescale cannot be determined with
precision, but amounts from one to several days. It could be related to
corotating interaction regions, known to exist in zeta Pup from UV
observations. Hour-long changes, linked to flares or to the pulsation activity,
are not observed in the last decade covered by the XMM observations; the 17h
tentative period, previously reported in a ROSAT analysis, is not confirmed
either and is thus transient, at best. On the other hand, short-term changes
are surprisingly small (<1% relative amplitude for the total energy band). In
fact, they are compatible solely with the presence of Poisson noise in the
data. This surprisingly low level of short-term variability, in view of the
embedded wind-shock origin, requires a very high fragmentation of the stellar
wind, for both absorbing and emitting features (>10^5 parcels, comparing with a
2D wind model). This is the first time that constraints have been placed on the
number of clumps in an O-type star wind and from X-ray observations.
Stellar winds are a crucial component of massive stars, but their exact
properties still remain uncertain. To shed some light on this subject, we have
analyzed an exceptional set of X-ray observations of zeya Pup, one of the
closest and brightest massive stars. The sensitive lightcurves that were
derived reveal two major results. On the one hand, a slow modulation of the
X-ray flux (with a relative amplitude of up to 15% over 16h in the 0.3--4.0keV
band) is detected. Its characteristic timescale cannot be determined with
precision, but amounts from one to several days. It could be related to
corotating interaction regions, known to exist in zeta Pup from UV
observations. Hour-long changes, linked to flares or to the pulsation activity,
are not observed in the last decade covered by the XMM observations; the 17h
tentative period, previously reported in a ROSAT analysis, is not confirmed
either and is thus transient, at best. On the other hand, short-term changes
are surprisingly small (<1% relative amplitude for the total energy band). In
fact, they are compatible solely with the presence of Poisson noise in the
data. This surprisingly low level of short-term variability, in view of the
embedded wind-shock origin, requires a very high fragmentation of the stellar
wind, for both absorbing and emitting features (>10^5 parcels, comparing with a
2D wind model). This is the first time that constraints have been placed on the
number of clumps in an O-type star wind and from X-ray observations.
Cosmological Evolution of Supermassive Black Holes: Mass Functions and Spins. (arXiv:1212.2187v1 [astro-ph.CO])
Cosmological Evolution of Supermassive Black Holes: Mass Functions and Spins. (arXiv:1212.2187v1 [astro-ph.CO]):
We derive the mass function of supermassive black holes (SMBHs) over the
redshift range 0<z<2, using the latest deep luminosity and mass functions of
field galaxies. Applying this mass function, combined with the bolometric
luminosity function of active galactic nuclei (AGNs), into the the continuity
equation of SMBH number density, we explicitly obtain the mass-dependent
cosmological evolution of the radiative efficiency for accretion. We suggest
that the accretion history of SMBHs and their spins evolve in two distinct
regimes: an early phase of prolonged accretion, plausibly driven by major
mergers, during which the black hole spins up, then switching to a period of
random, episodic accretion, governed by minor mergers and internal secular
processes, during which the hole spins down. The transition epoch depends on
mass, mirroring other evidence for "cosmic downsizing" in the AGN population.
We derive the mass function of supermassive black holes (SMBHs) over the
redshift range 0<z<2, using the latest deep luminosity and mass functions of
field galaxies. Applying this mass function, combined with the bolometric
luminosity function of active galactic nuclei (AGNs), into the the continuity
equation of SMBH number density, we explicitly obtain the mass-dependent
cosmological evolution of the radiative efficiency for accretion. We suggest
that the accretion history of SMBHs and their spins evolve in two distinct
regimes: an early phase of prolonged accretion, plausibly driven by major
mergers, during which the black hole spins up, then switching to a period of
random, episodic accretion, governed by minor mergers and internal secular
processes, during which the hole spins down. The transition epoch depends on
mass, mirroring other evidence for "cosmic downsizing" in the AGN population.
An X-ray study of the galactic-scale starburst-driven outflow in NGC 253. (arXiv:1212.1904v1 [astro-ph.CO])
An X-ray study of the galactic-scale starburst-driven outflow in NGC 253. (arXiv:1212.1904v1 [astro-ph.CO]):
X-ray properties of hot interstellar gas in a starburst galaxy NGC 253 were
investigated to gain a further understanding of starburst-driven outflow
activity by XMM-Newton and Suzaku. Spectroscopic analysis for three regions of
the galaxy characterized by multiwavelength observations was conducted. The hot
gas was represented by two thin thermal plasmas with temperatures of kT ~0.2
and ~0.6 keV. Abundance ratios i.e., O/Fe, Ne/Fe, Mg/Fe and Si/Fe, are
consistent between three regions, which suggests the common origin of the hot
gas. The abundance patterns are consistent with those of type II supernova
ejecta, indicating that the starburst activity in the central region provides
metals toward the halo through a galactic-scale starburst-driven outflow. The
energetics also can support this indication on condition that 0.01-50
{\eta}^0.5 % of the total emission in the nuclear region has flowed to the halo
region. To constrain the dynamics of hot interstellar gas, surface brightness
and hardness ratio profiles which trace the density and temperature were
extracted. Assuming a simple polytropic equation of state of gas,
T{\rho}^(1-{\gamma}) = const, we constrained the physical condition. {\gamma}
is consistent with 5/3 at the hot disk and T is constant ({\gamma} = 1) in the
halo. It is suggested that the hot gas expands adiabatically from the central
region towards the halo region while it moves as free expansion from the inner
part of the halo towards the outer part of the halo as the outflow. We
constrained the outflow velocity to be >100 km s^-1 from the observed
temperature gradient in the halo. In comparison with the escape velocity of
~220 km s^-1 for NGC 253, it is indicated that the hot interstellar gas can
escape from the gravitational potential of NGC 253 by combining the outflow
velocity and the thermal velocity.
X-ray properties of hot interstellar gas in a starburst galaxy NGC 253 were
investigated to gain a further understanding of starburst-driven outflow
activity by XMM-Newton and Suzaku. Spectroscopic analysis for three regions of
the galaxy characterized by multiwavelength observations was conducted. The hot
gas was represented by two thin thermal plasmas with temperatures of kT ~0.2
and ~0.6 keV. Abundance ratios i.e., O/Fe, Ne/Fe, Mg/Fe and Si/Fe, are
consistent between three regions, which suggests the common origin of the hot
gas. The abundance patterns are consistent with those of type II supernova
ejecta, indicating that the starburst activity in the central region provides
metals toward the halo through a galactic-scale starburst-driven outflow. The
energetics also can support this indication on condition that 0.01-50
{\eta}^0.5 % of the total emission in the nuclear region has flowed to the halo
region. To constrain the dynamics of hot interstellar gas, surface brightness
and hardness ratio profiles which trace the density and temperature were
extracted. Assuming a simple polytropic equation of state of gas,
T{\rho}^(1-{\gamma}) = const, we constrained the physical condition. {\gamma}
is consistent with 5/3 at the hot disk and T is constant ({\gamma} = 1) in the
halo. It is suggested that the hot gas expands adiabatically from the central
region towards the halo region while it moves as free expansion from the inner
part of the halo towards the outer part of the halo as the outflow. We
constrained the outflow velocity to be >100 km s^-1 from the observed
temperature gradient in the halo. In comparison with the escape velocity of
~220 km s^-1 for NGC 253, it is indicated that the hot interstellar gas can
escape from the gravitational potential of NGC 253 by combining the outflow
velocity and the thermal velocity.
Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy. (arXiv:1212.3475v1 [astro-ph.GA])
Limits on intermediate-mass black holes in six Galactic globular clusters with integral-field spectroscopy. (arXiv:1212.3475v1 [astro-ph.GA]):
The formation of supermassive black holes at high redshift still remains a
puzzle to astronomers. Their growth becomes reasonable only when starting from
a massive seed black hole with mass of the order of 10^2 - 10^5 M_SUN.
Intermediate-mass black holes (IMBHs) are therefore an important field of
research. Especially the possibility of finding them in the centers of globular
clusters has recently drawn attention. The search for IMBHs in the centers of
globular clusters could therefore shed light on the process of black-hole
formation and cluster evolution. We are investigating six galactic globular
clusters for the presence of an IMBH at their centers. Based on their kinematic
and photometric properties, we selected the globular clusters NGC 1851, NGC
1904 (M79), NGC 5694, NGC 5824, NGC 6093 (M80) and NGC 6266 (M62). We use
integral field spectroscopy in order to obtain the central velocity-dispersion
profile of each cluster. We compute the cluster photometric center and the
surface brightness profile using HST data. After combining these datasets we
compare them to analytic Jeans models. We use varying M/L_V profiles for
clusters with enough data points in order to reproduce their kinematic profiles
in an optimal way. Finally, we vary the mass of the central black hole and test
whether the cluster is better fitted with or without an IMBH. We present the
statistical significance, including upper limits, of the black-hole mass for
each cluster. NGC 1904 and NGC 6266 provide the highest significance for a
black hole. Jeans models in combination with a M/L_V profile obtained from
N-body simulations (in the case of NGC 6266) predict a central black hole of
M_BH = (3 +- 1) x 10^3 M_SUN for NGC 1904 and M_BH = (2 +- 1) x 10^3 M_SUN for
NGC 6266. Furthermore, we discuss the possible influence of dark remnants and
mass segregation at the center of the cluster on the detection of an IMBH.
The formation of supermassive black holes at high redshift still remains a
puzzle to astronomers. Their growth becomes reasonable only when starting from
a massive seed black hole with mass of the order of 10^2 - 10^5 M_SUN.
Intermediate-mass black holes (IMBHs) are therefore an important field of
research. Especially the possibility of finding them in the centers of globular
clusters has recently drawn attention. The search for IMBHs in the centers of
globular clusters could therefore shed light on the process of black-hole
formation and cluster evolution. We are investigating six galactic globular
clusters for the presence of an IMBH at their centers. Based on their kinematic
and photometric properties, we selected the globular clusters NGC 1851, NGC
1904 (M79), NGC 5694, NGC 5824, NGC 6093 (M80) and NGC 6266 (M62). We use
integral field spectroscopy in order to obtain the central velocity-dispersion
profile of each cluster. We compute the cluster photometric center and the
surface brightness profile using HST data. After combining these datasets we
compare them to analytic Jeans models. We use varying M/L_V profiles for
clusters with enough data points in order to reproduce their kinematic profiles
in an optimal way. Finally, we vary the mass of the central black hole and test
whether the cluster is better fitted with or without an IMBH. We present the
statistical significance, including upper limits, of the black-hole mass for
each cluster. NGC 1904 and NGC 6266 provide the highest significance for a
black hole. Jeans models in combination with a M/L_V profile obtained from
N-body simulations (in the case of NGC 6266) predict a central black hole of
M_BH = (3 +- 1) x 10^3 M_SUN for NGC 1904 and M_BH = (2 +- 1) x 10^3 M_SUN for
NGC 6266. Furthermore, we discuss the possible influence of dark remnants and
mass segregation at the center of the cluster on the detection of an IMBH.
Thursday, December 13, 2012
The Planck Sunyaev-Zel'dovich vs. the X-ray View of the Coma Cluster. (arXiv:1212.3082v1 [astro-ph.CO])
The Planck Sunyaev-Zel'dovich vs. the X-ray View of the Coma Cluster. (arXiv:1212.3082v1 [astro-ph.CO]):
The Planck collaboration has recently published precise and resolved
measurements of the Sunyaev-Zel'dovich effect in Abell 1656 (the Coma cluster
of galaxies), so directly gauging the electron pressure profile in the
intracluster plasma. On the other hand, such a quantity may be also derived
from combining the density and temperature provided by X-ray observations of
the thermal bremsstrahlung radiation emitted by the plasma. We find a
model-independent tension between the SZ and the X-ray pressure, with the SZ
one being definitely lower by 15-20%. We propose that such a challenging
tension can be resolved in terms of an additional, non-thermal support to the
gravitational equilibrium of the intracluster plasma. This can be
straightforwardly included in our Supermodel, so as to fit in detail the Planck
SZ profile while being consistent with the X-ray observables. Possible origins
of the nonthermal component include cosmic-ray protons, ongoing turbulence, and
relativistic electrons; given the existing observational constraints on the
first two options, here we focus on the third. For this to be effective, we
find that the electron population must include not only an energetic tail
accelerated to gamma> 10^3 responsible for the Coma radiohalo, but also many
more, lower energy electrons. The electron acceleration is to be started by
merging events similar to those which provided the very high central entropy of
the thermal intracluster plasma in Coma.
The Planck collaboration has recently published precise and resolved
measurements of the Sunyaev-Zel'dovich effect in Abell 1656 (the Coma cluster
of galaxies), so directly gauging the electron pressure profile in the
intracluster plasma. On the other hand, such a quantity may be also derived
from combining the density and temperature provided by X-ray observations of
the thermal bremsstrahlung radiation emitted by the plasma. We find a
model-independent tension between the SZ and the X-ray pressure, with the SZ
one being definitely lower by 15-20%. We propose that such a challenging
tension can be resolved in terms of an additional, non-thermal support to the
gravitational equilibrium of the intracluster plasma. This can be
straightforwardly included in our Supermodel, so as to fit in detail the Planck
SZ profile while being consistent with the X-ray observables. Possible origins
of the nonthermal component include cosmic-ray protons, ongoing turbulence, and
relativistic electrons; given the existing observational constraints on the
first two options, here we focus on the third. For this to be effective, we
find that the electron population must include not only an energetic tail
accelerated to gamma> 10^3 responsible for the Coma radiohalo, but also many
more, lower energy electrons. The electron acceleration is to be started by
merging events similar to those which provided the very high central entropy of
the thermal intracluster plasma in Coma.
Constraints on Hydrodynamical Subgrid Models from Quasar Absorption Line Studies of the Simulated Circumgalactic Medium. (arXiv:1212.2965v1 [astro-ph.GA])
Constraints on Hydrodynamical Subgrid Models from Quasar Absorption Line Studies of the Simulated Circumgalactic Medium. (arXiv:1212.2965v1 [astro-ph.GA]):
Cosmological hydrodynamical simulations of galaxy evolution are increasingly
able to produce realistic galaxies, but the largest hurdle remaining is in
constructing subgrid models that accurately describe the behavior of stellar
feedback. As an alternate way to test and calibrate such models, we propose to
focus on the circumgalactic medium. To do so, we generate a suite of
adaptive-mesh refinement (AMR) simulations for a Milky-Way-massed galaxy run to
z=0, systematically varying the feedback implementation. We then post-process
the simulation data to compute the absorbing column density for a wide range of
common atomic absorbers throughout the galactic halo, including H I, Mg II, Si
II, Si III, Si IV, C IV, N V, O VI, and O VII. The radial profiles of these
atomic column densities are compared against several quasar absorption line
studies, to determine if one feedback prescription is favored. We find that
although our models match some of the observations (specifically those ions
with lower ionization strengths), it is particularly difficult to match O VI
observations. There is some indication that the models with increased feedback
intensity are better matches. We demonstrate that sufficient metals exist in
these halos to reproduce the observed column density distribution in principle,
but the simulated circumgalactic medium lacks significant multiphase
substructure and is generally too hot. Furthermore, we demonstrate the failings
of inflow-only models (without energetic feedback) at populating the CGM with
adequate metals to match observations even in the presence of multiphase
structure. Additionally, we briefly investigate the evolution of the CGM from
z=3 to present. Overall, we find that quasar absorption line observations of
the gas around galaxies provide a new and important constraint on feedback
models.
Cosmological hydrodynamical simulations of galaxy evolution are increasingly
able to produce realistic galaxies, but the largest hurdle remaining is in
constructing subgrid models that accurately describe the behavior of stellar
feedback. As an alternate way to test and calibrate such models, we propose to
focus on the circumgalactic medium. To do so, we generate a suite of
adaptive-mesh refinement (AMR) simulations for a Milky-Way-massed galaxy run to
z=0, systematically varying the feedback implementation. We then post-process
the simulation data to compute the absorbing column density for a wide range of
common atomic absorbers throughout the galactic halo, including H I, Mg II, Si
II, Si III, Si IV, C IV, N V, O VI, and O VII. The radial profiles of these
atomic column densities are compared against several quasar absorption line
studies, to determine if one feedback prescription is favored. We find that
although our models match some of the observations (specifically those ions
with lower ionization strengths), it is particularly difficult to match O VI
observations. There is some indication that the models with increased feedback
intensity are better matches. We demonstrate that sufficient metals exist in
these halos to reproduce the observed column density distribution in principle,
but the simulated circumgalactic medium lacks significant multiphase
substructure and is generally too hot. Furthermore, we demonstrate the failings
of inflow-only models (without energetic feedback) at populating the CGM with
adequate metals to match observations even in the presence of multiphase
structure. Additionally, we briefly investigate the evolution of the CGM from
z=3 to present. Overall, we find that quasar absorption line observations of
the gas around galaxies provide a new and important constraint on feedback
models.
Wednesday, December 12, 2012
Insights into thermonuclear supernovae from the incomplete silicon burning process. (arXiv:1212.2410v1 [astro-ph.SR])
Insights into thermonuclear supernovae from the incomplete silicon burning process. (arXiv:1212.2410v1 [astro-ph.SR]):
Type Ia supernova (SNIa) explosions synthesize a few tenths to several tenths
of a solar mass, whose composition is the result of incomplete silicon burning
that reaches peak temperatures of 4 GK to 5 GK. The elemental abundances are
sensitive to the physical conditions in the explosion, making their measurement
a promising clue to uncovering the properties of the progenitor star and of the
explosion itself. Using a parameterized description of the thermodynamic
history of matter undergoing incomplete silicon burning, we computed the final
composition for a range of parameters wide enough to encompass current models
of SNIa. Then, we searched for combinations of elemental abundances that trace
the parameters values and are potentially measurable. For this purpose, we
divide the present study into two epochs of SNIa, namely the optical epoch,
from a few weeks to several months after the explosion, and the X-ray epoch,
which refers to the time period in which the supernova remnant is young,
starting one or two hundred years age and ending a thousand years after the
event. During the optical epoch, the only SNIa property that can be extracted
from the detection of incomplete silicon burning elements is the neutron excess
of the progenitor white dwarf at thermal runaway, which can be determined
through measuring the ratio of the abundance of manganese to that of titanium,
chromium, or vanadium. Conversely, in the X-ray epoch, any abundance ratio
built using a couple of elements from titanium, vanadium, chromium, or
manganese may constrain the initial neutron excess. Furthermore, measuring the
ratio of the abundances of vanadium to manganese in the X-ray might shed light
on the timescale of the thermonuclear explosion.
Type Ia supernova (SNIa) explosions synthesize a few tenths to several tenths
of a solar mass, whose composition is the result of incomplete silicon burning
that reaches peak temperatures of 4 GK to 5 GK. The elemental abundances are
sensitive to the physical conditions in the explosion, making their measurement
a promising clue to uncovering the properties of the progenitor star and of the
explosion itself. Using a parameterized description of the thermodynamic
history of matter undergoing incomplete silicon burning, we computed the final
composition for a range of parameters wide enough to encompass current models
of SNIa. Then, we searched for combinations of elemental abundances that trace
the parameters values and are potentially measurable. For this purpose, we
divide the present study into two epochs of SNIa, namely the optical epoch,
from a few weeks to several months after the explosion, and the X-ray epoch,
which refers to the time period in which the supernova remnant is young,
starting one or two hundred years age and ending a thousand years after the
event. During the optical epoch, the only SNIa property that can be extracted
from the detection of incomplete silicon burning elements is the neutron excess
of the progenitor white dwarf at thermal runaway, which can be determined
through measuring the ratio of the abundance of manganese to that of titanium,
chromium, or vanadium. Conversely, in the X-ray epoch, any abundance ratio
built using a couple of elements from titanium, vanadium, chromium, or
manganese may constrain the initial neutron excess. Furthermore, measuring the
ratio of the abundances of vanadium to manganese in the X-ray might shed light
on the timescale of the thermonuclear explosion.
Parameters of rotating neutron stars with and without hyperons. (arXiv:1212.2369v1 [astro-ph.SR])
Parameters of rotating neutron stars with and without hyperons. (arXiv:1212.2369v1 [astro-ph.SR]):
The discovery of a 2 Msun neutron star provided a robust constraint for the
theory of exotic dense matter, questioning the existence of strange baryons in
the interiors of neutron stars. With many theories failing to reproduce this
observational result, several equations of state containing hyperons are
consistent with it. We study global properties of stars using equations of
state containing hyperons, and compare them to those without hyperons in order
to find similarities, differences and limits that can be compared with the
astrophysical observations. Rotating, axisymmetric and stationary stellar
configurations in General Relativity are obtained, and their global parameters
are studied. Approximate formulae describing the behavior of the maximum and
minimum stellar mass, compactness, surface redshifts and moments of inertia as
functions of spin frequency are provided. We also study the thin disk accretion
and compare the spin-up evolution of stars with different moments of inertia.
The discovery of a 2 Msun neutron star provided a robust constraint for the
theory of exotic dense matter, questioning the existence of strange baryons in
the interiors of neutron stars. With many theories failing to reproduce this
observational result, several equations of state containing hyperons are
consistent with it. We study global properties of stars using equations of
state containing hyperons, and compare them to those without hyperons in order
to find similarities, differences and limits that can be compared with the
astrophysical observations. Rotating, axisymmetric and stationary stellar
configurations in General Relativity are obtained, and their global parameters
are studied. Approximate formulae describing the behavior of the maximum and
minimum stellar mass, compactness, surface redshifts and moments of inertia as
functions of spin frequency are provided. We also study the thin disk accretion
and compare the spin-up evolution of stars with different moments of inertia.
Recurrent novae as progenitors of Type Ia supernovae. (arXiv:1212.2295v1 [astro-ph.SR])
Recurrent novae as progenitors of Type Ia supernovae. (arXiv:1212.2295v1 [astro-ph.SR]):
Recurrent novae are binaries harboring a very massive white dwarf (WD), as
massive as the Chandrasekhar mass, because of their short recurrence periods of
nova outbursts of 10-100 years. Thus, recurrent novae are considered as
candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia
PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The
binary parameters of recurrent novae have been well determined, especially for
the ones with frequent outbursts, U Sco and RS Oph, which provide useful
information on the elementary processes in binary evolution toward SNe Ia.
Therefore we use them as testbeds for binary evolution models. For example, the
original double degenerate (DD) scenario cannot reproduce RS Oph type recurrent
novae, whereas the new single degenerate (SD) scenario proposed by Hachisu et
al. (1999) naturally can. We review main differences between the SD and DD
scenarios, especially for their basic processes of binary evolution. We also
discuss observational support for each physical process. The original DD
scenario is based on the physics in 1980s, whereas the SD scenario on more
recent physics including the new opacity, mass-growth efficiency of WDs, and
optically thick winds developed in nova outbursts.
Recurrent novae are binaries harboring a very massive white dwarf (WD), as
massive as the Chandrasekhar mass, because of their short recurrence periods of
nova outbursts of 10-100 years. Thus, recurrent novae are considered as
candidates of progenitors of Type Ia supernovae (SNe Ia). In fact, the SN Ia
PTF11kx showed evidence that its progenitor is a symbiotic recurrent nova. The
binary parameters of recurrent novae have been well determined, especially for
the ones with frequent outbursts, U Sco and RS Oph, which provide useful
information on the elementary processes in binary evolution toward SNe Ia.
Therefore we use them as testbeds for binary evolution models. For example, the
original double degenerate (DD) scenario cannot reproduce RS Oph type recurrent
novae, whereas the new single degenerate (SD) scenario proposed by Hachisu et
al. (1999) naturally can. We review main differences between the SD and DD
scenarios, especially for their basic processes of binary evolution. We also
discuss observational support for each physical process. The original DD
scenario is based on the physics in 1980s, whereas the SD scenario on more
recent physics including the new opacity, mass-growth efficiency of WDs, and
optically thick winds developed in nova outbursts.
Characterization of ICM Temperature Distributions of 62 Galaxy Clusters with XMM-Newton. (arXiv:1212.2239v1 [astro-ph.CO])
Characterization of ICM Temperature Distributions of 62 Galaxy Clusters with XMM-Newton. (arXiv:1212.2239v1 [astro-ph.CO]):
We measure the intracluster medium temperature distributions for 62 galaxy
clusters in the HIFLUGCS, an X-ray flux-limited sample, with available X-ray
data from XMM-Newton. We search for correlations between the width of the
temperature distributions and other cluster properties, including median
cluster temperature, luminosity, size, presence of a cool core, AGN activity,
and dynamical state. We use a Markov Chain Monte Carlo analysis which models
the ICM as a collection of X-ray emitting smoothed particles of plasma. Each
smoothed particle is given its own set of parameters, including temperature,
spatial position, redshift, size, and emission measure. This allows us to
measure the width of the temperature distribution, median temperature, and
total emission measure of each cluster. We find that none of the clusters have
a temperature width, \sigma_kT, consistent with isothermality.
Counterintuitively, we also find that the temperature distribution widths of
disturbed, non-cool-core, and AGN-free clusters tend to be wider than in other
clusters. A linear fit to \sigma_kT - kT_med finds \sigma_kT ~ 0.20kT_med +
1.08, with an estimated intrinsic scatter of ~ 0.55 keV, demonstrating a large
range in ICM thermal histories.
We measure the intracluster medium temperature distributions for 62 galaxy
clusters in the HIFLUGCS, an X-ray flux-limited sample, with available X-ray
data from XMM-Newton. We search for correlations between the width of the
temperature distributions and other cluster properties, including median
cluster temperature, luminosity, size, presence of a cool core, AGN activity,
and dynamical state. We use a Markov Chain Monte Carlo analysis which models
the ICM as a collection of X-ray emitting smoothed particles of plasma. Each
smoothed particle is given its own set of parameters, including temperature,
spatial position, redshift, size, and emission measure. This allows us to
measure the width of the temperature distribution, median temperature, and
total emission measure of each cluster. We find that none of the clusters have
a temperature width, \sigma_kT, consistent with isothermality.
Counterintuitively, we also find that the temperature distribution widths of
disturbed, non-cool-core, and AGN-free clusters tend to be wider than in other
clusters. A linear fit to \sigma_kT - kT_med finds \sigma_kT ~ 0.20kT_med +
1.08, with an estimated intrinsic scatter of ~ 0.55 keV, demonstrating a large
range in ICM thermal histories.
Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1. (arXiv:1212.2218v1 [astro-ph.CO])
Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1. (arXiv:1212.2218v1 [astro-ph.CO]):
We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional "BPT" line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/\Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic BPT diagnostic ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha)
remains consistent with X-ray AGN/SF classification. The X-ray data also
suggest that "composite" galaxies (with intermediate AGN/SF classification)
host bona-fide AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have
nuclear activity detected by either X-rays or the BPT diagnostic. Compared to
the X-ray and BPT classifications, the mass-excitation method remains effective
at z>1, but we show that the color-excitation method requires a new calibration
to successfully identify AGNs at these redshifts.
We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional "BPT" line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/\Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic BPT diagnostic ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha)
remains consistent with X-ray AGN/SF classification. The X-ray data also
suggest that "composite" galaxies (with intermediate AGN/SF classification)
host bona-fide AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have
nuclear activity detected by either X-rays or the BPT diagnostic. Compared to
the X-ray and BPT classifications, the mass-excitation method remains effective
at z>1, but we show that the color-excitation method requires a new calibration
to successfully identify AGNs at these redshifts.
The origin of the lag spectra observed in AGN: Reverberation and the propagation of X-ray source fluctuations. (arXiv:1212.2213v1 [astro-ph.HE])
The origin of the lag spectra observed in AGN: Reverberation and the propagation of X-ray source fluctuations. (arXiv:1212.2213v1 [astro-ph.HE]):
The X-ray emission from active galactic nuclei (AGN) is highly variable.
Measurements of time lags (characterised by lag spectra) between variability in
the light curves in energy bands corresponding to directly observed continuum
emission from the corona around the black hole and to X-rays reflected from the
accretion disc adds a further dimension to studies of the structure and
energetics of these systems. We seek to understand these measurements in terms
of the physical parameters of the X-ray source (its location, extent, etc.)
through the calculation of theoretical lag spectra for a range of source
parameters in general relativistic ray tracing simulations, combined with
knowledge of the observed variability of the X-ray emission from AGN. Due to
the proximity of the emission to the central black hole, Shapiro delays are
important and the effects of general relativity should be considered when
interpreting the lags as the light travel time between the source and
reflector. We show that it is important to consider dilution of the lag by the
contribution of both the primary and reflected spectral components to the
observed energy bands. We find that the observed lag spectrum of the narrow
line Seyfert 1 galaxy 1H 0707-495 implies an X-ray source extending radially
outwards to around 35rg and at a height of around 2rg above the plane of the
accretion disc, consistent with the constraints obtained independently by
considering the emissivity profile of the accretion disc. By investigating the
influence of the propagation of X-ray luminosity fluctuations through the
source region we find it is possible to reproduce the shape of the low
frequency part of the lag spectrum (where the hard 'primary' band lags behind
the soft 'reflected' band) as the effect of luminosity fluctuations originating
in the centre of the X-ray source, close to the black hole, and propagating
outwards.
The X-ray emission from active galactic nuclei (AGN) is highly variable.
Measurements of time lags (characterised by lag spectra) between variability in
the light curves in energy bands corresponding to directly observed continuum
emission from the corona around the black hole and to X-rays reflected from the
accretion disc adds a further dimension to studies of the structure and
energetics of these systems. We seek to understand these measurements in terms
of the physical parameters of the X-ray source (its location, extent, etc.)
through the calculation of theoretical lag spectra for a range of source
parameters in general relativistic ray tracing simulations, combined with
knowledge of the observed variability of the X-ray emission from AGN. Due to
the proximity of the emission to the central black hole, Shapiro delays are
important and the effects of general relativity should be considered when
interpreting the lags as the light travel time between the source and
reflector. We show that it is important to consider dilution of the lag by the
contribution of both the primary and reflected spectral components to the
observed energy bands. We find that the observed lag spectrum of the narrow
line Seyfert 1 galaxy 1H 0707-495 implies an X-ray source extending radially
outwards to around 35rg and at a height of around 2rg above the plane of the
accretion disc, consistent with the constraints obtained independently by
considering the emissivity profile of the accretion disc. By investigating the
influence of the propagation of X-ray luminosity fluctuations through the
source region we find it is possible to reproduce the shape of the low
frequency part of the lag spectrum (where the hard 'primary' band lags behind
the soft 'reflected' band) as the effect of luminosity fluctuations originating
in the centre of the X-ray source, close to the black hole, and propagating
outwards.
Type Iax Supernovae: A New Class of Stellar Explosion. (arXiv:1212.2209v1 [astro-ph.SR])
Type Iax Supernovae: A New Class of Stellar Explosion. (arXiv:1212.2209v1 [astro-ph.SR]):
We describe observed properties of the Type Iax class of supernovae (SNe
Iax), consisting of SNe observationally similar to its prototypical member, SN
2002cx. The class currently has 25 members, and we present optical photometry
and/or optical spectroscopy for most of them. SNe Iax are spectroscopically
similar to SNe Ia, but have lower maximum-light velocities (2000 < |v| < 8000
km/s), typically lower peak magnitudes (-14.2 > M_V,peak > -18.9 mag), and most
have hot photospheres. Relative to SNe Ia, SNe Iax have low luminosities for
their light-curve shape. There is a correlation between luminosity and
light-curve shape, similar to that of SNe Ia, but offset from that of SNe Ia
and with larger scatter. Despite a host-galaxy morphology distribution that is
highly skewed to late-type galaxies without any SNe Iax discovered in
elliptical galaxies, there are several indications that the progenitor stars
are white dwarfs (WDs): evidence of C/O burning in their maximum-light spectra,
low ejecta masses, strong Fe lines in their late-time spectra, a lack of X-ray
detections, and deep limits on massive stars and star formation at the SN
sites. However, two SNe Iax show strong He lines in their spectra. The
progenitor system and explosion model that best fits all of the data is a
binary system of a C/O WD that accretes matter from a He star and has a
significant deflagration. At least some of the time, this explosion will not
disrupt the WD. We estimate that in a given volume there are 31^+17_-13 SNe Iax
for every 100 SNe Ia, and for every 1 M_sun of iron generated by SNe Ia at z =
0, SNe Iax generate 0.052^+0.017_-0.014 M_sun. Being the largest class of
peculiar SNe, thousands of SNe Iax will be discovered by LSST. Future detailed
observations of SNe Iax should further our understanding of both their
progenitor systems and explosions as well as those of SNe Ia.
We describe observed properties of the Type Iax class of supernovae (SNe
Iax), consisting of SNe observationally similar to its prototypical member, SN
2002cx. The class currently has 25 members, and we present optical photometry
and/or optical spectroscopy for most of them. SNe Iax are spectroscopically
similar to SNe Ia, but have lower maximum-light velocities (2000 < |v| < 8000
km/s), typically lower peak magnitudes (-14.2 > M_V,peak > -18.9 mag), and most
have hot photospheres. Relative to SNe Ia, SNe Iax have low luminosities for
their light-curve shape. There is a correlation between luminosity and
light-curve shape, similar to that of SNe Ia, but offset from that of SNe Ia
and with larger scatter. Despite a host-galaxy morphology distribution that is
highly skewed to late-type galaxies without any SNe Iax discovered in
elliptical galaxies, there are several indications that the progenitor stars
are white dwarfs (WDs): evidence of C/O burning in their maximum-light spectra,
low ejecta masses, strong Fe lines in their late-time spectra, a lack of X-ray
detections, and deep limits on massive stars and star formation at the SN
sites. However, two SNe Iax show strong He lines in their spectra. The
progenitor system and explosion model that best fits all of the data is a
binary system of a C/O WD that accretes matter from a He star and has a
significant deflagration. At least some of the time, this explosion will not
disrupt the WD. We estimate that in a given volume there are 31^+17_-13 SNe Iax
for every 100 SNe Ia, and for every 1 M_sun of iron generated by SNe Ia at z =
0, SNe Iax generate 0.052^+0.017_-0.014 M_sun. Being the largest class of
peculiar SNe, thousands of SNe Iax will be discovered by LSST. Future detailed
observations of SNe Iax should further our understanding of both their
progenitor systems and explosions as well as those of SNe Ia.
Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO])
Ca, Fe, and Mg Trends Among and Within Elliptical Galaxies. (arXiv:1212.2675v1 [astro-ph.CO]):
In a sample of elliptical galaxies that span a large range of mass, a
previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically
decrease with increasing elliptical galaxy mass. Metallicity mixtures, age
effects, stellar chromospheric emission effects, and low-mass initial mass
function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less
than 0.3 dex is sufficient to blanket all observations. Feature gradients
within galaxies imply a global Ca deficit rather than a radius-dependent
phenomenon. Some, but not all, Type II supernova nucleosynthetic yield
calculations indicate a decreasing Ca/Fe yield ratio in more massive
supernovae, lending possible support to the hypothesis that more massive
elliptical galaxies have an IMF that favors more massive stars. No Type II
supernova nucleosynthetic yield calculations show significant leverage in the
Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems
unlikely that the Ca behavior can be explained as a built-in metallicity
effect, and this argues against explanations that vary only the Type II to Type
Ia supernova enrichment ratio.
In a sample of elliptical galaxies that span a large range of mass, a
previously unused Ca index, CaHK, shows that [Ca/Fe] and [Ca/Mg] systematically
decrease with increasing elliptical galaxy mass. Metallicity mixtures, age
effects, stellar chromospheric emission effects, and low-mass initial mass
function (IMF) boost effects are ruled out as causes. A [Ca/Fe] range of less
than 0.3 dex is sufficient to blanket all observations. Feature gradients
within galaxies imply a global Ca deficit rather than a radius-dependent
phenomenon. Some, but not all, Type II supernova nucleosynthetic yield
calculations indicate a decreasing Ca/Fe yield ratio in more massive
supernovae, lending possible support to the hypothesis that more massive
elliptical galaxies have an IMF that favors more massive stars. No Type II
supernova nucleosynthetic yield calculations show significant leverage in the
Ca/Fe ratio as a function of progenitor metallicity. Therefore, it seems
unlikely that the Ca behavior can be explained as a built-in metallicity
effect, and this argues against explanations that vary only the Type II to Type
Ia supernova enrichment ratio.
Chandra observations of SN 1987A: the soft X-ray light curve revisited. (arXiv:1212.2664v1 [astro-ph.HE])
Chandra observations of SN 1987A: the soft X-ray light curve revisited. (arXiv:1212.2664v1 [astro-ph.HE]):
We report on the present stage of SN 1987A as observed by the Chandra X-ray
Observatory. We reanalyze published Chandra observations and add three more
epochs of Chandra data to get a consistent picture of the evolution of the
X-ray fluxes in several energy bands. We discuss the implications of several
calibration issues for Chandra data. Using the most recent Chandra calibration
files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by
~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our
previous result that the 0.5-2.0 keV light curve showed a sudden flattening in
2009. Based on our new analysis, we conclude that the forward shock is still in
full interaction with the equatorial ring.
We report on the present stage of SN 1987A as observed by the Chandra X-ray
Observatory. We reanalyze published Chandra observations and add three more
epochs of Chandra data to get a consistent picture of the evolution of the
X-ray fluxes in several energy bands. We discuss the implications of several
calibration issues for Chandra data. Using the most recent Chandra calibration
files, we find that the 0.5-2.0 keV band fluxes of SN 1987A have increased by
~6 x 10 ^-13 erg s^-1 cm^-2 per year since 2009. This is in contrast with our
previous result that the 0.5-2.0 keV light curve showed a sudden flattening in
2009. Based on our new analysis, we conclude that the forward shock is still in
full interaction with the equatorial ring.
Accretion disks around black holes in modified strong gravity. (arXiv:1212.2640v1 [astro-ph.CO])
Accretion disks around black holes in modified strong gravity. (arXiv:1212.2640v1 [astro-ph.CO]):
Stellar-mass black holes offer what is perhaps the best scenario to test
theories of gravity in the strong-field regime. In particular, f(R) theories,
which have been widely discuss in a cosmological context, can be constrained
through realistic astrophysical models of phenomena around black holes. We aim
at building radiative models of thin accretion disks for both Schwarzschild and
Kerr black holes in f(R) gravity. We study particle motion in
f(R)-Schwarzschild and Kerr space-times. We present the spectral energy
distribution of the accretion disk around constant Ricci scalar f(R) black
holes, and constrain specific f(R) prescriptions using features of these
systems. A precise determination of both the spin and accretion rate onto black
holes along with X-ray observations of their thermal spectrum might allow to
identify deviations of gravity from General Relativity. We use recent data on
the high-mass X-ray binary Cygnus X-1 to restrict the values of the parameters
of a class of f(R) models.
Stellar-mass black holes offer what is perhaps the best scenario to test
theories of gravity in the strong-field regime. In particular, f(R) theories,
which have been widely discuss in a cosmological context, can be constrained
through realistic astrophysical models of phenomena around black holes. We aim
at building radiative models of thin accretion disks for both Schwarzschild and
Kerr black holes in f(R) gravity. We study particle motion in
f(R)-Schwarzschild and Kerr space-times. We present the spectral energy
distribution of the accretion disk around constant Ricci scalar f(R) black
holes, and constrain specific f(R) prescriptions using features of these
systems. A precise determination of both the spin and accretion rate onto black
holes along with X-ray observations of their thermal spectrum might allow to
identify deviations of gravity from General Relativity. We use recent data on
the high-mass X-ray binary Cygnus X-1 to restrict the values of the parameters
of a class of f(R) models.
Tuesday, December 11, 2012
Connecting neutron star observations to the high density equation of state of quasi-particle model. (arXiv:1212.1749v1 [astro-ph.HE])
Connecting neutron star observations to the high density equation of state of quasi-particle model. (arXiv:1212.1749v1 [astro-ph.HE]):
The observation of $1.97\pm0.04$ solar-mass neutron-like star gives
constraint on the equation of state (EOS) of cold, condensed matter. In this
paper, the EOS for both pure quark star and hybrid star with a quark core
described by quasi-particle model are considered. The parameters of
quasi-particle model which affect the mass of both quark star and hybrid star
can be constrained by the observation.
The observation of $1.97\pm0.04$ solar-mass neutron-like star gives
constraint on the equation of state (EOS) of cold, condensed matter. In this
paper, the EOS for both pure quark star and hybrid star with a quark core
described by quasi-particle model are considered. The parameters of
quasi-particle model which affect the mass of both quark star and hybrid star
can be constrained by the observation.
Friday, December 7, 2012
Intragroup and Galaxy-Linked Diffuse X-ray Emission in Hickson Compact Groups. (arXiv:1212.1151v1 [astro-ph.CO])
Intragroup and Galaxy-Linked Diffuse X-ray Emission in Hickson Compact Groups. (arXiv:1212.1151v1 [astro-ph.CO]):
Isolated compact groups of galaxies (CGs) present a range of dynamical
states, group velocity dispersions, and galaxy morphologies with which to study
galaxy evolution, particularly the properties of gas both within the galaxies
and in the intragroup medium. As part of a large, multiwavelength examination
of CGs, we present an archival study of diffuse X-ray emission in a subset of
nine Hickson compact groups observed with the Chandra X-ray Observatory. We
find that seven of the groups in our sample exhibit detectable diffuse
emission. However, unlike large-scale emission in galaxy clusters, the diffuse
features in the majority of the detected groups are linked to the individual
galaxies, in the form of both plumes and halos likely as a result of star
formation or AGN activity, as well as in emission from tidal features. Unlike
previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found
to be consistent with the Lx-T relationship from clusters within the errors,
while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though
this is likely coincidental given that the hot gas in these two systems is
largely due to star formation. We find that Lx increases with decreasing group
HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray
luminosity on HI morphology whereby systems with intragroup HI indicative of
strong interactions are considerably more X-ray luminous than passively
evolving groups. We also find a gap in the Lx of groups as a function of the
total group specific star formation rate. Our findings suggest that the hot gas
in these groups is not in hydrostatic equilibrium and these systems are not
low-mass analogs of rich groups or clusters, with the possible exception of HCG
62.
Isolated compact groups of galaxies (CGs) present a range of dynamical
states, group velocity dispersions, and galaxy morphologies with which to study
galaxy evolution, particularly the properties of gas both within the galaxies
and in the intragroup medium. As part of a large, multiwavelength examination
of CGs, we present an archival study of diffuse X-ray emission in a subset of
nine Hickson compact groups observed with the Chandra X-ray Observatory. We
find that seven of the groups in our sample exhibit detectable diffuse
emission. However, unlike large-scale emission in galaxy clusters, the diffuse
features in the majority of the detected groups are linked to the individual
galaxies, in the form of both plumes and halos likely as a result of star
formation or AGN activity, as well as in emission from tidal features. Unlike
previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found
to be consistent with the Lx-T relationship from clusters within the errors,
while HCGs 16 and 31 are consistent with the cluster Lx-sigma relation, though
this is likely coincidental given that the hot gas in these two systems is
largely due to star formation. We find that Lx increases with decreasing group
HI to dynamical-mass ratio with tentative evidence for a dependance in X-ray
luminosity on HI morphology whereby systems with intragroup HI indicative of
strong interactions are considerably more X-ray luminous than passively
evolving groups. We also find a gap in the Lx of groups as a function of the
total group specific star formation rate. Our findings suggest that the hot gas
in these groups is not in hydrostatic equilibrium and these systems are not
low-mass analogs of rich groups or clusters, with the possible exception of HCG
62.
Thursday, December 6, 2012
Can Superflares Occur on Our Sun?. (arXiv:1212.1361v1 [astro-ph.SR])
Can Superflares Occur on Our Sun?. (arXiv:1212.1361v1 [astro-ph.SR]):
Recent observations of solar type stars with the Kepler satellite by Maehara
et al. have revealed the existence of superflares (with energy of 10^33 - 10^35
erg) on Sun-like stars, which are similar to our Sun in their surface
temperature (5600 K - 6000 K) and slow rotation (rotational period > 10 days).
From the statistical analysis of these superflares, it was found that
superflares with energy 10^34 erg occur once in 800 years and superflares with
10^35 erg occur once in 5000 years on Sun-like stars. In this paper, we examine
whether superflares with energy of 10^33 - 10^35 erg could occur on the present
Sun through the use of simple order-of-magnitude estimates based on current
ideas relating to the mechanisms of the solar dynamo.
Recent observations of solar type stars with the Kepler satellite by Maehara
et al. have revealed the existence of superflares (with energy of 10^33 - 10^35
erg) on Sun-like stars, which are similar to our Sun in their surface
temperature (5600 K - 6000 K) and slow rotation (rotational period > 10 days).
From the statistical analysis of these superflares, it was found that
superflares with energy 10^34 erg occur once in 800 years and superflares with
10^35 erg occur once in 5000 years on Sun-like stars. In this paper, we examine
whether superflares with energy of 10^33 - 10^35 erg could occur on the present
Sun through the use of simple order-of-magnitude estimates based on current
ideas relating to the mechanisms of the solar dynamo.
Probing Nuclear Symmetry Energy and its Imprints on Properties of Nuclei, Nuclear Reactions, Neutron Stars and Gravitational Waves. (arXiv:1212.1178v1 [nucl-th])
Probing Nuclear Symmetry Energy and its Imprints on Properties of Nuclei, Nuclear Reactions, Neutron Stars and Gravitational Waves. (arXiv:1212.1178v1 [nucl-th]):
Significant progress has been made in recent years in constraining nuclear
symmetry energy at and below the saturation density of nuclear matter using
data from both terrestrial nuclear experiments and astrophysical observations.
However, many interesting questions remain to be studied especially at
supra-saturation densities. In this lecture note, after a brief summary of the
currently available constraints on nuclear symmetry energy near the saturation
density we first discuss the relationship between the symmetry energy and the
isopin and momentum dependence of the single-nucleon potential in
isospin-asymmetric nuclear medium. We then discuss several open issues
regarding effects of the tensor force induced neutron-proton short-range
correlation (SRC) on nuclear symmetry energy. Finally, as an example of the
impacts of nuclear symmetry energy on properties of neutron stars and
gravitational waves, we illustrate effects of the high-density symmetry energy
on the tidal polarizability of neutron stars in coalescing binaries.
Significant progress has been made in recent years in constraining nuclear
symmetry energy at and below the saturation density of nuclear matter using
data from both terrestrial nuclear experiments and astrophysical observations.
However, many interesting questions remain to be studied especially at
supra-saturation densities. In this lecture note, after a brief summary of the
currently available constraints on nuclear symmetry energy near the saturation
density we first discuss the relationship between the symmetry energy and the
isopin and momentum dependence of the single-nucleon potential in
isospin-asymmetric nuclear medium. We then discuss several open issues
regarding effects of the tensor force induced neutron-proton short-range
correlation (SRC) on nuclear symmetry energy. Finally, as an example of the
impacts of nuclear symmetry energy on properties of neutron stars and
gravitational waves, we illustrate effects of the high-density symmetry energy
on the tidal polarizability of neutron stars in coalescing binaries.
Variability of a stellar corona on a time scale of days. (arXiv:1212.0214v1 [astro-ph.SR])
Variability of a stellar corona on a time scale of days. (arXiv:1212.0214v1 [astro-ph.SR]):
Elemental abundance effects in active coronae have eluded our understanding
for almost three decades, since the discovery of the First Ionization Potential
(FIP) effect on the sun. The goal of this paper is to monitor the same coronal
structures over a time interval of six days and resolve active regions on a
stellar corona through rotational modulation. We report on four iso-phase X-ray
spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried
out approximately every two days, to match the rotation period of EI Eri. We
present an analysis of the thermal and chemical structure of the Ei Eri corona
as it evolves over the six days. Although the corona is rather steady in its
temperature distribution, the emission measure and FIP bias both vary and seem
to be correlated. An active region, predating the beginning of the campaign,
repeatedly enters into our view at the same phase as it rotates from beyond the
stellar limb. As a result, the abundances tend slightly, but consistently, to
increase for high FIP elements (an inverse FIP effect) with phase. We estimate
the abundance increase of high FIP elements in the active region to be of ~75%
over the coronal mean. This observed fractionation of elements in an active
region on time scales of days provides circumstantial clues regarding the
element enrichment mechanism of non-flaring stellar coronae.
Elemental abundance effects in active coronae have eluded our understanding
for almost three decades, since the discovery of the First Ionization Potential
(FIP) effect on the sun. The goal of this paper is to monitor the same coronal
structures over a time interval of six days and resolve active regions on a
stellar corona through rotational modulation. We report on four iso-phase X-ray
spectroscopic observations of the RS CVn binary EI Eri with XMM-Newton, carried
out approximately every two days, to match the rotation period of EI Eri. We
present an analysis of the thermal and chemical structure of the Ei Eri corona
as it evolves over the six days. Although the corona is rather steady in its
temperature distribution, the emission measure and FIP bias both vary and seem
to be correlated. An active region, predating the beginning of the campaign,
repeatedly enters into our view at the same phase as it rotates from beyond the
stellar limb. As a result, the abundances tend slightly, but consistently, to
increase for high FIP elements (an inverse FIP effect) with phase. We estimate
the abundance increase of high FIP elements in the active region to be of ~75%
over the coronal mean. This observed fractionation of elements in an active
region on time scales of days provides circumstantial clues regarding the
element enrichment mechanism of non-flaring stellar coronae.
Magnetized hot neutron matter: lowest order constrained variational calculations. (arXiv:1212.0784v1 [nucl-th])
Magnetized hot neutron matter: lowest order constrained variational calculations. (arXiv:1212.0784v1 [nucl-th]):
We have studied the spin polarized hot neutron matter in the presence of
strong magnetic field. In this work, using the lowest order constrained
variational method at finite temperature and employing $AV_{18}$ nuclear
potential, some thermodynamic properties of spin polarized neutron matter such
as spin polarization parameter, free energy, equation of state and effective
mass have been calculated. It has been shown that the strong magnetic field
breaks the symmetry of the free energy, leading to a magnetized equilibrium
state. We have found that the equation of state becomes stiffer by increasing
both magnetic field and temperature. The magnetic field dependence of effective
mass for the spin-up and spin-down neutrons has been investigated.
We have studied the spin polarized hot neutron matter in the presence of
strong magnetic field. In this work, using the lowest order constrained
variational method at finite temperature and employing $AV_{18}$ nuclear
potential, some thermodynamic properties of spin polarized neutron matter such
as spin polarization parameter, free energy, equation of state and effective
mass have been calculated. It has been shown that the strong magnetic field
breaks the symmetry of the free energy, leading to a magnetized equilibrium
state. We have found that the equation of state becomes stiffer by increasing
both magnetic field and temperature. The magnetic field dependence of effective
mass for the spin-up and spin-down neutrons has been investigated.
Emission lines between 1 and 2 keV in Cometary X-ray Spectra. (arXiv:1212.0624v1 [astro-ph.EP])
Emission lines between 1 and 2 keV in Cometary X-ray Spectra. (arXiv:1212.0624v1 [astro-ph.EP]):
We present the detection of new cometary X-ray emission lines in the 1.0 to
2.0 keV range using a sample of comets observed with the Chandra X-ray
observatory and ACIS spectrometer. We have selected 5 comets from the Chandra
sample with good signal-to-noise spectra. The surveyed comets are: C/1999 S4
(LINEAR), C/1999 T1 (McNaught-Hartley), 153P/2002 (Ikeya-Zhang), 2P/2003
(Encke), and C/2008 8P (Tuttle). We modeled the spectra with an extended
version of our solar wind charge exchange (SWCX) emission model (Bodewits et
al. 2007). Above 1 keV, we find Ikeya-Zhang to have strong emission lines at
1340 and 1850 eV that we identify as being created by solar wind charge
exchange lines of Mg XI and Si XIII, respectively, and weaker emission lines at
1470, 1600, and 1950 eV formed by SWCX of Mg XII, Mg XI, and Si XIV,
respectively. The Mg XI and XII and Si XIII and XIV lines are detected at a
significant level for the other comets in our sample (LS4, MH, Encke, 8P), and
these lines promise additional diagnostics to be included in SWCX models. The
silicon lines in the 1700 to 2000 eV range are detected for all comets, but
with the rising background and decreasing cometary emission, we caution these
detections need further confirmation with higher resolution instruments.
We present the detection of new cometary X-ray emission lines in the 1.0 to
2.0 keV range using a sample of comets observed with the Chandra X-ray
observatory and ACIS spectrometer. We have selected 5 comets from the Chandra
sample with good signal-to-noise spectra. The surveyed comets are: C/1999 S4
(LINEAR), C/1999 T1 (McNaught-Hartley), 153P/2002 (Ikeya-Zhang), 2P/2003
(Encke), and C/2008 8P (Tuttle). We modeled the spectra with an extended
version of our solar wind charge exchange (SWCX) emission model (Bodewits et
al. 2007). Above 1 keV, we find Ikeya-Zhang to have strong emission lines at
1340 and 1850 eV that we identify as being created by solar wind charge
exchange lines of Mg XI and Si XIII, respectively, and weaker emission lines at
1470, 1600, and 1950 eV formed by SWCX of Mg XII, Mg XI, and Si XIV,
respectively. The Mg XI and XII and Si XIII and XIV lines are detected at a
significant level for the other comets in our sample (LS4, MH, Encke, 8P), and
these lines promise additional diagnostics to be included in SWCX models. The
silicon lines in the 1700 to 2000 eV range are detected for all comets, but
with the rising background and decreasing cometary emission, we caution these
detections need further confirmation with higher resolution instruments.
Clusters of galaxies and variation of the fine structure constant. (arXiv:1212.1075v1 [astro-ph.CO])
Clusters of galaxies and variation of the fine structure constant. (arXiv:1212.1075v1 [astro-ph.CO]):
We propose a new method to probe for variations in the fine structure
constant alpha using clusters of galaxies, opening up a window on a new
redshift range for such constraints. Hot clusters shine in the X-ray mainly due
to bremsstrahlung, while they leave an imprint on the CMB frequency spectrum
through the Sunyaev-Zel'dovich effect. These two physical processes can be
characterized by the integrated Comptonization parameter Y_SZ DA^2 and its
X-ray counterpart, the Y_X parameter. The ratio of these two quantities is
expected to be constant from numerical simulations and current observations. We
show that this fact can be exploited to constrain alpha, as the ratio of the
two parameters depends on the fine structure constant as alpha^{3.5}. We
determine current constraints from a combination of Planck SZ and XMM-Newton
data, testing different models of variation of alpha. When fitting for a
constant value of alpha, we find that current constraints are at the 1% level,
comparable with current CMB constraints. We discuss strategies for further
improving these constraints by almost an order of magnitude.
We propose a new method to probe for variations in the fine structure
constant alpha using clusters of galaxies, opening up a window on a new
redshift range for such constraints. Hot clusters shine in the X-ray mainly due
to bremsstrahlung, while they leave an imprint on the CMB frequency spectrum
through the Sunyaev-Zel'dovich effect. These two physical processes can be
characterized by the integrated Comptonization parameter Y_SZ DA^2 and its
X-ray counterpart, the Y_X parameter. The ratio of these two quantities is
expected to be constant from numerical simulations and current observations. We
show that this fact can be exploited to constrain alpha, as the ratio of the
two parameters depends on the fine structure constant as alpha^{3.5}. We
determine current constraints from a combination of Planck SZ and XMM-Newton
data, testing different models of variation of alpha. When fitting for a
constant value of alpha, we find that current constraints are at the 1% level,
comparable with current CMB constraints. We discuss strategies for further
improving these constraints by almost an order of magnitude.
The mass ejection from the merger of binary neutron stars. (arXiv:1212.0905v1 [astro-ph.HE])
The mass ejection from the merger of binary neutron stars. (arXiv:1212.0905v1 [astro-ph.HE]):
Numerical-relativity simulations for the merger of binary neutron stars are
performed for a variety of equations of state (EOSs) and for a plausible range
of the neutron-star mass, focusing primarily on the properties of the material
ejected from the system. We find that a fraction of the material is ejected as
a mildly relativistic and mildly anisotropic outflow with the typical and
maximum velocities $\sim 0.15$ -- $0.25c$ and $\sim 0.5$ -- $0.8c$ (where $c$
is the speed of light), respectively, and that the total ejected rest mass is
in a wide range $10^{-4}$ -- $10^{-2}M_{\odot}$, which depends strongly on the
EOS, the total mass, and the mass ratio. The total kinetic energy ejected is
also in a wide range between $10^{49}$ and $10^{51} {\rm ergs}$. The numerical
results suggest that for a binary of canonical total mass $2.7M_{\odot}$, the
outflow could generate an electromagnetic signal observable by the planned
telescopes through the production of heavy-element unstable nuclei via the
$r$-process or through the formation of blast waves during the interaction with
the interstellar matter, if the EOS and mass of the binary are favorable ones.
Numerical-relativity simulations for the merger of binary neutron stars are
performed for a variety of equations of state (EOSs) and for a plausible range
of the neutron-star mass, focusing primarily on the properties of the material
ejected from the system. We find that a fraction of the material is ejected as
a mildly relativistic and mildly anisotropic outflow with the typical and
maximum velocities $\sim 0.15$ -- $0.25c$ and $\sim 0.5$ -- $0.8c$ (where $c$
is the speed of light), respectively, and that the total ejected rest mass is
in a wide range $10^{-4}$ -- $10^{-2}M_{\odot}$, which depends strongly on the
EOS, the total mass, and the mass ratio. The total kinetic energy ejected is
also in a wide range between $10^{49}$ and $10^{51} {\rm ergs}$. The numerical
results suggest that for a binary of canonical total mass $2.7M_{\odot}$, the
outflow could generate an electromagnetic signal observable by the planned
telescopes through the production of heavy-element unstable nuclei via the
$r$-process or through the formation of blast waves during the interaction with
the interstellar matter, if the EOS and mass of the binary are favorable ones.
Quark matter symmetry energy and quark stars. (arXiv:1212.1388v1 [astro-ph.SR])
Quark matter symmetry energy and quark stars. (arXiv:1212.1388v1 [astro-ph.SR]):
We extend the confined-density-dependent-mass model to include isospin
dependence of the equivalent quark mass. Within the
confined-isospin-density-dependent-mass model, we study the quark matter
symmetry energy, the stability of strange quark matter, and the properties of
quark stars. We find that including isospin dependence of the equivalent quark
mass can significantly enhance the quark matter symmetry energy and stiffen
strange quark matter. The recently discovered large mass pulsar PSR J1614-2230
with a mass of $1.97\pm0.04M_{\odot}$ can be well described by a quark star if
the equivalent quark mass is strongly isospin dependent, indicating that the
quark matter symmetry energy might be much stronger than the nuclear matter
symmetry energy.
We extend the confined-density-dependent-mass model to include isospin
dependence of the equivalent quark mass. Within the
confined-isospin-density-dependent-mass model, we study the quark matter
symmetry energy, the stability of strange quark matter, and the properties of
quark stars. We find that including isospin dependence of the equivalent quark
mass can significantly enhance the quark matter symmetry energy and stiffen
strange quark matter. The recently discovered large mass pulsar PSR J1614-2230
with a mass of $1.97\pm0.04M_{\odot}$ can be well described by a quark star if
the equivalent quark mass is strongly isospin dependent, indicating that the
quark matter symmetry energy might be much stronger than the nuclear matter
symmetry energy.
Velocity width measurements of the coolest X-ray emitting material in the cores of clusters, groups and elliptical galaxies. (arXiv:1212.1259v1 [astro-ph.CO])
Velocity width measurements of the coolest X-ray emitting material in the cores of clusters, groups and elliptical galaxies. (arXiv:1212.1259v1 [astro-ph.CO]):
We examine the velocity width of cool X-ray emitting material using
XMM-Newton Reflection Grating Spectrometer (RGS) spectra of a sample of
clusters and group of galaxies and elliptical galaxies. Improving on our
previous analyses, we apply a spectral model which accounts for broadening due
to the spatial extent of the source. With both conventional and Markov Chain
Monte Carlo approaches we obtain limits, or in a few cases measurements, of the
velocity broadening of the coolest X-ray material. In our sample, we include
new observations targeting objects with compact, bright, line-rich cores. One
of these, MACSJ2229.7-2755, gives a velocity limit of 280 km/s at the 90 per
cent confidence level. Other systems with limits close to 300 km/s include
A1835, NGC4261 and NGC4472. For more than a third of the targets we find limits
better than 500 km/s. HCG62, NGC1399 and A3112 show evidence for ~400 km/s
velocity broadening. For a smaller sample of objects, we use
continuum-subtracted emission line surface brightness profiles to account for
the spatial broadening. Although there are significant systematic errors
associated with the technique (~150 km/s), we find broadening at the level of
280 to 500 km/s in A3112, NGC1399 and NGC4636.
We examine the velocity width of cool X-ray emitting material using
XMM-Newton Reflection Grating Spectrometer (RGS) spectra of a sample of
clusters and group of galaxies and elliptical galaxies. Improving on our
previous analyses, we apply a spectral model which accounts for broadening due
to the spatial extent of the source. With both conventional and Markov Chain
Monte Carlo approaches we obtain limits, or in a few cases measurements, of the
velocity broadening of the coolest X-ray material. In our sample, we include
new observations targeting objects with compact, bright, line-rich cores. One
of these, MACSJ2229.7-2755, gives a velocity limit of 280 km/s at the 90 per
cent confidence level. Other systems with limits close to 300 km/s include
A1835, NGC4261 and NGC4472. For more than a third of the targets we find limits
better than 500 km/s. HCG62, NGC1399 and A3112 show evidence for ~400 km/s
velocity broadening. For a smaller sample of objects, we use
continuum-subtracted emission line surface brightness profiles to account for
the spatial broadening. Although there are significant systematic errors
associated with the technique (~150 km/s), we find broadening at the level of
280 to 500 km/s in A3112, NGC1399 and NGC4636.
Monday, December 3, 2012
A sample of Seyfert-2 galaxies with ultra-luminous galaxy-wide NLRs -- Quasar light echos?. (arXiv:1211.7098v1 [astro-ph.CO])
A sample of Seyfert-2 galaxies with ultra-luminous galaxy-wide NLRs -- Quasar light echos?. (arXiv:1211.7098v1 [astro-ph.CO]):
We report the discovery of Seyfert-2 galaxies in SDSS-DR8 with galaxy-wide,
ultra-luminous narrow-line regions (NLRs) at redshifts z=0.2-0.6. With a space
density of 4.4 per cubic Gpc at z~0.3, these "Green Beans" (GBs) are amongst
the rarest objects in the Universe. We are witnessing an exceptional and/or
short-lived phenomenon in the life cycle of AGN. The main focus of this paper
is on a detailed analysis of the GB prototype galaxy J2240-0927 (z=0.326). Its
NLR extends over 26x44 kpc and is surrounded by an extended narrow-line region
(ENLR). With a total [OIII]5008 luminosity of (5.7+/-0.9)x10e43 erg/s, this is
one of the most luminous NLR known around any type-2 galaxy. Using VLT/XSHOOTER
we show that the NLR is powered by an AGN, and we derive resolved extinction,
density and ionization maps. Gas kinematics is disturbed on a global scale, and
high velocity outflows are absent or faint. This NLR is unlike any other NLR or
extended emission line region (EELR) known. Spectroscopy with Gemini/GMOS
reveals extended, high luminosity [OIII] emission also in other GBs. WISE
24micron luminosities are 5-50 times lower than predicted by the [OIII] fluxes,
suggesting that the NLRs reflect earlier, very active quasar states that have
strongly subsided in less than a galaxies' light crossing time. These light
echos are about 100 times more luminous than any other such light echo known to
date. X-ray data are needed for photo-ionization modeling and to verify the
light echos.
We report the discovery of Seyfert-2 galaxies in SDSS-DR8 with galaxy-wide,
ultra-luminous narrow-line regions (NLRs) at redshifts z=0.2-0.6. With a space
density of 4.4 per cubic Gpc at z~0.3, these "Green Beans" (GBs) are amongst
the rarest objects in the Universe. We are witnessing an exceptional and/or
short-lived phenomenon in the life cycle of AGN. The main focus of this paper
is on a detailed analysis of the GB prototype galaxy J2240-0927 (z=0.326). Its
NLR extends over 26x44 kpc and is surrounded by an extended narrow-line region
(ENLR). With a total [OIII]5008 luminosity of (5.7+/-0.9)x10e43 erg/s, this is
one of the most luminous NLR known around any type-2 galaxy. Using VLT/XSHOOTER
we show that the NLR is powered by an AGN, and we derive resolved extinction,
density and ionization maps. Gas kinematics is disturbed on a global scale, and
high velocity outflows are absent or faint. This NLR is unlike any other NLR or
extended emission line region (EELR) known. Spectroscopy with Gemini/GMOS
reveals extended, high luminosity [OIII] emission also in other GBs. WISE
24micron luminosities are 5-50 times lower than predicted by the [OIII] fluxes,
suggesting that the NLRs reflect earlier, very active quasar states that have
strongly subsided in less than a galaxies' light crossing time. These light
echos are about 100 times more luminous than any other such light echo known to
date. X-ray data are needed for photo-ionization modeling and to verify the
light echos.
Saturday, December 1, 2012
Three-dimensional delayed-detonation models with nucleosynthesis for Type Ia supernovae. (arXiv:1211.3015v1 [astro-ph.SR])
Three-dimensional delayed-detonation models with nucleosynthesis for Type Ia supernovae. (arXiv:1211.3015v1 [astro-ph.SR]):
We present results for a suite of fourteen three-dimensional, high resolution
hydrodynamical simulations of delayed-detonation modelsof Type Ia supernova (SN
Ia) explosions. This model suite comprises the first set of three-dimensional
SN Ia simulations with detailed isotopic yield information. As such, it may
serve as a database for Chandrasekhar-mass delayed-detonation model
nucleosynthetic yields and for deriving synthetic observables such as spectra
and light curves. We employ a physically motivated, stochastic model based on
turbulent velocity fluctuations and fuel density to calculate in situ the
deflagration to detonation transition (DDT) probabilities. To obtain different
strengths of the deflagration phase and thereby different degrees of
pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10,
20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition
kernels in a hydrostatic white dwarf with central density of 2.9 x 10^9 gcc,
plus in addition one high central density (5.5 x 10^9 gcc), and one low central
density (1.0 x 10^9 gcc) rendition of the 100 ignition kernel configuration.
For each simulation we determined detailed nucleosynthetic yields by
post-processing 10^6 tracer particles with a 384 nuclide reaction network. All
delayed detonation models result in explosions unbinding the white dwarf,
producing a range of 56Ni masses from 0.32 to 1.11 solar masses. As a general
trend, the models predict that the stable neutron-rich iron group isotopes are
not found at the lowest velocities, but rather at intermediate velocities
(~3,000 - 10,000 km/s) in a shell surrounding a 56Ni-rich core. The models
further predict relatively low velocity oxygen and carbon, with typical minimum
velocities around 4,000 and 10,000 km/s, respectively.
We present results for a suite of fourteen three-dimensional, high resolution
hydrodynamical simulations of delayed-detonation modelsof Type Ia supernova (SN
Ia) explosions. This model suite comprises the first set of three-dimensional
SN Ia simulations with detailed isotopic yield information. As such, it may
serve as a database for Chandrasekhar-mass delayed-detonation model
nucleosynthetic yields and for deriving synthetic observables such as spectra
and light curves. We employ a physically motivated, stochastic model based on
turbulent velocity fluctuations and fuel density to calculate in situ the
deflagration to detonation transition (DDT) probabilities. To obtain different
strengths of the deflagration phase and thereby different degrees of
pre-expansion, we have chosen a sequence of initial models with 1, 3, 5, 10,
20, 40, 100, 150, 200, 300, and 1600 (two different realizations) ignition
kernels in a hydrostatic white dwarf with central density of 2.9 x 10^9 gcc,
plus in addition one high central density (5.5 x 10^9 gcc), and one low central
density (1.0 x 10^9 gcc) rendition of the 100 ignition kernel configuration.
For each simulation we determined detailed nucleosynthetic yields by
post-processing 10^6 tracer particles with a 384 nuclide reaction network. All
delayed detonation models result in explosions unbinding the white dwarf,
producing a range of 56Ni masses from 0.32 to 1.11 solar masses. As a general
trend, the models predict that the stable neutron-rich iron group isotopes are
not found at the lowest velocities, but rather at intermediate velocities
(~3,000 - 10,000 km/s) in a shell surrounding a 56Ni-rich core. The models
further predict relatively low velocity oxygen and carbon, with typical minimum
velocities around 4,000 and 10,000 km/s, respectively.
Bias from gas inhomogeneities in the pressure profiles as measured from X-ray and SZ observations. (arXiv:1211.3358v1 [astro-ph.CO])
Bias from gas inhomogeneities in the pressure profiles as measured from X-ray and SZ observations. (arXiv:1211.3358v1 [astro-ph.CO]):
X-ray observations of galaxy clusters provide emission measure weighted
spectra, arising from a range of density and temperature fluctuations in the
intra-cluster medium (ICM). This is fitted to a single temperature plasma
emission model to provide an estimate of the gas density and temperature, which
are sensitive to the gas inhomogeneities. Therefore, X-ray observations yield a
potentially biased estimate of the thermal gas pressure, P_X. At the same time
Sunyaev-Zeldovich (SZ) observations directly measure the integrated gas
pressure, P_SZ. If the X-ray pressure profiles are strongly biased with respect
to to the SZ, then one has the possibility to probe the gas inhomogeneities,
even at scales unresolved by the current generation of telescopes. At the same
time, a weak bias has implications for the use of mass proxies like Y_SZ and
Y_X as cosmological probes. In this paper we investigate the dependence of the
bias, P_X(r)/P_SZ(r)-1, on the characteristics of fluctuations in the ICM
taking into account the correlation between temperature and density
fluctuations. We made a simple prediction of the irreducible bias in idealised
X-ray vs SZ observations using multi-temperature plasma emission model. We also
provide a simple fitting form to estimate the bias given the distribution of
fluctuations. Analysing a sample of 16 simulated clusters extracted from
hydrodynamical simulations, we find that the median value of bias is within
+/-3% within R_500, it decreases to -5% at R_500 < r < 1.5R_500 and then rises
back to ~0% at > 2R_500. The scatter of b_P(r) between individual relaxed
clusters is small -- at the level of <0.03 within R_500, but turns
significantly larger (0.25) and highly skewed at r > 1.5 R_500. Unrelaxed
clusters display larger scatter (both from radius to radius and from cluster to
cluster). Nevertheless, the bias remains within +/-20% within 0.8R_500 for all
clusters.
X-ray observations of galaxy clusters provide emission measure weighted
spectra, arising from a range of density and temperature fluctuations in the
intra-cluster medium (ICM). This is fitted to a single temperature plasma
emission model to provide an estimate of the gas density and temperature, which
are sensitive to the gas inhomogeneities. Therefore, X-ray observations yield a
potentially biased estimate of the thermal gas pressure, P_X. At the same time
Sunyaev-Zeldovich (SZ) observations directly measure the integrated gas
pressure, P_SZ. If the X-ray pressure profiles are strongly biased with respect
to to the SZ, then one has the possibility to probe the gas inhomogeneities,
even at scales unresolved by the current generation of telescopes. At the same
time, a weak bias has implications for the use of mass proxies like Y_SZ and
Y_X as cosmological probes. In this paper we investigate the dependence of the
bias, P_X(r)/P_SZ(r)-1, on the characteristics of fluctuations in the ICM
taking into account the correlation between temperature and density
fluctuations. We made a simple prediction of the irreducible bias in idealised
X-ray vs SZ observations using multi-temperature plasma emission model. We also
provide a simple fitting form to estimate the bias given the distribution of
fluctuations. Analysing a sample of 16 simulated clusters extracted from
hydrodynamical simulations, we find that the median value of bias is within
+/-3% within R_500, it decreases to -5% at R_500 < r < 1.5R_500 and then rises
back to ~0% at > 2R_500. The scatter of b_P(r) between individual relaxed
clusters is small -- at the level of <0.03 within R_500, but turns
significantly larger (0.25) and highly skewed at r > 1.5 R_500. Unrelaxed
clusters display larger scatter (both from radius to radius and from cluster to
cluster). Nevertheless, the bias remains within +/-20% within 0.8R_500 for all
clusters.
Seeking for the leading actor on the cosmic stage: Galaxies versus Supermassive Black Holes. (arXiv:1211.3258v1 [astro-ph.CO])
Seeking for the leading actor on the cosmic stage: Galaxies versus Supermassive Black Holes. (arXiv:1211.3258v1 [astro-ph.CO]):
We present a Special Issue on the interplay of galaxies and Supermassive
Black Holes (SMBHs) recently published in Advances in Astronomy. This is the
introductory paper containing the motivation for this Special Issue together
with a brief description of the articles which are part of the manuscript and
the link to the entire book (this http URL). We
hope this Special Issue will be useful for many astronomers who want to get an
update on the current status of the AGN-Galaxy coevolution topic.
We present a Special Issue on the interplay of galaxies and Supermassive
Black Holes (SMBHs) recently published in Advances in Astronomy. This is the
introductory paper containing the motivation for this Special Issue together
with a brief description of the articles which are part of the manuscript and
the link to the entire book (this http URL). We
hope this Special Issue will be useful for many astronomers who want to get an
update on the current status of the AGN-Galaxy coevolution topic.
Identification of members in the central and outer regions of galaxy clusters. (arXiv:1211.3669v1 [astro-ph.CO])
Identification of members in the central and outer regions of galaxy clusters. (arXiv:1211.3669v1 [astro-ph.CO]):
The caustic technique measures the mass of galaxy clusters in both their
virial and infall regions and, as a byproduct, yields the list of cluster
galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h
extracted from a cosmological N-body simulation of a LambdaCDM universe to test
the ability of the caustic technique to identify the cluster galaxy members. We
identify the true three-dimensional members as the gravitationally bound
galaxies. The caustic technique uses the caustic location in the redshift
diagram to separate the cluster members from the interlopers. We apply the
technique to mock catalogues containing 1000 galaxies in the field of view of
12 Mpc/h on a side at the cluster location. On average, this sample size
roughly corresponds to 180 real galaxy members within 3r200, similar to recent
redshift surveys of cluster regions. The caustic technique yields a
completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within
3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to
fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of
the members of a galaxy cluster provides such large completeness and small
contamination at these large radii. The caustic technique assumes spherical
symmetry and the asphericity of the cluster is responsible for most of the
spread of the completeness and the contamination. By applying the technique to
an approximately spherical system obtained by stacking the individual clusters,
the spreads decrease by at least a factor of two. We finally estimate the
cluster mass within 3r200 after removing the interlopers: for individual
clusters, the mass estimated with the virial theorem is unbiased and within 30
per cent of the actual mass; this spread decreases to less than 10 per cent for
the spherically symmetric stacked cluster.
Note: Describes how well cluster masses can be derived from optical measurements, useful to know as a comparison to X-ray approaches
The caustic technique measures the mass of galaxy clusters in both their
virial and infall regions and, as a byproduct, yields the list of cluster
galaxy members. Here we use 100 galaxy clusters with mass M200>=1E14 Msun/h
extracted from a cosmological N-body simulation of a LambdaCDM universe to test
the ability of the caustic technique to identify the cluster galaxy members. We
identify the true three-dimensional members as the gravitationally bound
galaxies. The caustic technique uses the caustic location in the redshift
diagram to separate the cluster members from the interlopers. We apply the
technique to mock catalogues containing 1000 galaxies in the field of view of
12 Mpc/h on a side at the cluster location. On average, this sample size
roughly corresponds to 180 real galaxy members within 3r200, similar to recent
redshift surveys of cluster regions. The caustic technique yields a
completeness, the fraction of identified true members, fc=0.95 (+- 0.03) within
3r200. The contamination increases from fi=0.020 (+0.046;-0.015) at r200 to
fi=0.08 (+0.11;-0.05) at 3r200. No other technique for the identification of
the members of a galaxy cluster provides such large completeness and small
contamination at these large radii. The caustic technique assumes spherical
symmetry and the asphericity of the cluster is responsible for most of the
spread of the completeness and the contamination. By applying the technique to
an approximately spherical system obtained by stacking the individual clusters,
the spreads decrease by at least a factor of two. We finally estimate the
cluster mass within 3r200 after removing the interlopers: for individual
clusters, the mass estimated with the virial theorem is unbiased and within 30
per cent of the actual mass; this spread decreases to less than 10 per cent for
the spherically symmetric stacked cluster.
Note: Describes how well cluster masses can be derived from optical measurements, useful to know as a comparison to X-ray approaches
Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes. (arXiv:1211.3651v1 [astro-ph.CO])
Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes. (arXiv:1211.3651v1 [astro-ph.CO]):
Accreting black holes (BHs) produce intense radiation and powerful
relativistic jets, which are affected by the BH's spin magnitude and direction.
While thin disks might align with the BH spin axis via the Bardeen-Petterson
effect, this does not apply to jet systems with thick disks. We used fully
three-dimensional general relativistic magnetohydrodynamical simulations to
study accreting BHs with various BH spin vectors and disk thicknesses with
magnetic flux reaching saturation. Our simulations reveal a "magneto-spin
alignment" mechanism that causes magnetized disks and jets to align with the BH
spin near BHs and further away to reorient with the outer disk. This mechanism
has implications for the evolution of BH mass and spin, BH feedback on host
galaxies, and resolved BH images for SgrA* and M87.
Accreting black holes (BHs) produce intense radiation and powerful
relativistic jets, which are affected by the BH's spin magnitude and direction.
While thin disks might align with the BH spin axis via the Bardeen-Petterson
effect, this does not apply to jet systems with thick disks. We used fully
three-dimensional general relativistic magnetohydrodynamical simulations to
study accreting BHs with various BH spin vectors and disk thicknesses with
magnetic flux reaching saturation. Our simulations reveal a "magneto-spin
alignment" mechanism that causes magnetized disks and jets to align with the BH
spin near BHs and further away to reorient with the outer disk. This mechanism
has implications for the evolution of BH mass and spin, BH feedback on host
galaxies, and resolved BH images for SgrA* and M87.
X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*. (arXiv:1211.4529v1 [astro-ph.GA])
X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*. (arXiv:1211.4529v1 [astro-ph.GA]):
This paper presents the Suzaku results obtained for the Sagittarius (Sgr) C
region using the concept of X-ray reflection nebulae (XRNe) as the echo of past
flares from the super massive black hole, Sgr A*. The Sgr C complex is composed
of several molecular clouds proximately located in projected distance. The
X-ray spectra of Sgr C were analyzed on the basis of a view that XRNe are
located inside the Galactic center plasma X-ray emission with an oval
distribution around Sgr A*. We found that the XRNe are largely separated in the
line-of-sight position, and are associated with molecular clouds in different
velocity ranges detected by radio observations. We also applied the same
analysis to the Sgr B XRNe and completed a long-term light curve for Sgr A*
occurring in the past. As a new finding, we determined that Sgr A* was
experiencing periods of high luminosity already 500 years ago, which is longer
than the previously reported value. Our results are consistent with a scenario
that Sgr A* was continuously active with sporadic flux variabilities of Lx =
1-3 x 10^39 erg s^-1 in the past 50 to 500 years. The average past luminosity
was approximately 4-6 orders of magnitude higher than that presently observed.
In addition, two short-term flares of 5-10 years are found. Thus, the past
X-ray flare should not be a single short-term flare, but can be interpreted as
multiple flares superposed on a long-term high state.
This paper presents the Suzaku results obtained for the Sagittarius (Sgr) C
region using the concept of X-ray reflection nebulae (XRNe) as the echo of past
flares from the super massive black hole, Sgr A*. The Sgr C complex is composed
of several molecular clouds proximately located in projected distance. The
X-ray spectra of Sgr C were analyzed on the basis of a view that XRNe are
located inside the Galactic center plasma X-ray emission with an oval
distribution around Sgr A*. We found that the XRNe are largely separated in the
line-of-sight position, and are associated with molecular clouds in different
velocity ranges detected by radio observations. We also applied the same
analysis to the Sgr B XRNe and completed a long-term light curve for Sgr A*
occurring in the past. As a new finding, we determined that Sgr A* was
experiencing periods of high luminosity already 500 years ago, which is longer
than the previously reported value. Our results are consistent with a scenario
that Sgr A* was continuously active with sporadic flux variabilities of Lx =
1-3 x 10^39 erg s^-1 in the past 50 to 500 years. The average past luminosity
was approximately 4-6 orders of magnitude higher than that presently observed.
In addition, two short-term flares of 5-10 years are found. Thus, the past
X-ray flare should not be a single short-term flare, but can be interpreted as
multiple flares superposed on a long-term high state.
X-ray measurement of the elemental abundances at the outskirts of the Perseus cluster with Suzaku. (arXiv:1211.4712v1 [astro-ph.CO])
X-ray measurement of the elemental abundances at the outskirts of the Perseus cluster with Suzaku. (arXiv:1211.4712v1 [astro-ph.CO]):
We report on the abundance of metals (Mg and Fe) in the intracluster medium
(ICM) at the outskirts (0.2 r200 - 0.8 r200) of the Perseus cluster. The X-ray
spectra were obtained in the Suzaku/XIS mapping observations of this region. We
employ single temperature models to fit all the X-ray spectra. The ICM
temperature smoothly decreases toward the outer region from 6 keV to 4 keV. The
Fe abundance is uniformly distributed at the outskirts (~0.3 solar). The Mg
abundance is ~1 solar at the outskirts. The solar ratios of Mg/Fe of the
outskirts region (Mg/Fe ~4) are a factor of 4 larger than those of the central
region. Various systematic effects, including the spatial fluctuations in the
cosmic X-ray background, are taken into account and evaluated. These our
results have not changed significantly.
We report on the abundance of metals (Mg and Fe) in the intracluster medium
(ICM) at the outskirts (0.2 r200 - 0.8 r200) of the Perseus cluster. The X-ray
spectra were obtained in the Suzaku/XIS mapping observations of this region. We
employ single temperature models to fit all the X-ray spectra. The ICM
temperature smoothly decreases toward the outer region from 6 keV to 4 keV. The
Fe abundance is uniformly distributed at the outskirts (~0.3 solar). The Mg
abundance is ~1 solar at the outskirts. The solar ratios of Mg/Fe of the
outskirts region (Mg/Fe ~4) are a factor of 4 larger than those of the central
region. Various systematic effects, including the spatial fluctuations in the
cosmic X-ray background, are taken into account and evaluated. These our
results have not changed significantly.
Search for serendipitous TNO occultation in X-rays. (arXiv:1211.4650v1 [astro-ph.EP])
Search for serendipitous TNO occultation in X-rays. (arXiv:1211.4650v1 [astro-ph.EP]):
To study the population properties of small, remote objects beyond Neptune's
orbit in the outer solar system, of kilometer size or smaller, serendipitous
occultation search is so far the only way. For hectometer-sized Trans-Neptunian
Objects (TNOs), optical shadows actually disappear because of diffraction.
Observations at shorter wave lengths are needed. Here we report the effort of
TNO occultation search in X-rays using RXTE/PCA data of Sco X-1 taken from June
2007 to October 2011. No definite TNO occultation events were found in the 334
ks data. We investigate the detection efficiency dependence on the TNO size to
better define the sensible size range of our approach and suggest upper limits
to the TNO size distribution in the size range from 30 m to 300 m. A list of
X-ray sources suitable for future larger facilities to observe is proposed.
To study the population properties of small, remote objects beyond Neptune's
orbit in the outer solar system, of kilometer size or smaller, serendipitous
occultation search is so far the only way. For hectometer-sized Trans-Neptunian
Objects (TNOs), optical shadows actually disappear because of diffraction.
Observations at shorter wave lengths are needed. Here we report the effort of
TNO occultation search in X-rays using RXTE/PCA data of Sco X-1 taken from June
2007 to October 2011. No definite TNO occultation events were found in the 334
ks data. We investigate the detection efficiency dependence on the TNO size to
better define the sensible size range of our approach and suggest upper limits
to the TNO size distribution in the size range from 30 m to 300 m. A list of
X-ray sources suitable for future larger facilities to observe is proposed.
Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction. (arXiv:1211.4626v1 [astro-ph.CO])
Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction. (arXiv:1211.4626v1 [astro-ph.CO]):
We present Chandra X-ray measurements of the gas mass fraction out to r500
for a complete sample of the 35 most luminous clusters from the Brightest
Cluster Sample and the Extended Brightest Cluster Sample at redshift
z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data
were analysed independently using two pipelines and two different models for
the gas density and temperature. We measure an average of fgas(r500) = 0.163
+/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b /
Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar
baryon fraction. Earlier studies reported gas mass fractions significantly
lower than the cosmic baryon fraction at r500, and in some cases higher values
that are consistent with the cosmic baryon fraction towards the virial
radius.In this paper we show that the most X-ray luminous clusters in the
redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the
cosmic value at r500.
We present Chandra X-ray measurements of the gas mass fraction out to r500
for a complete sample of the 35 most luminous clusters from the Brightest
Cluster Sample and the Extended Brightest Cluster Sample at redshift
z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data
were analysed independently using two pipelines and two different models for
the gas density and temperature. We measure an average of fgas(r500) = 0.163
+/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b /
Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar
baryon fraction. Earlier studies reported gas mass fractions significantly
lower than the cosmic baryon fraction at r500, and in some cases higher values
that are consistent with the cosmic baryon fraction towards the virial
radius.In this paper we show that the most X-ray luminous clusters in the
redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the
cosmic value at r500.
The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays. (arXiv:1211.4590v1 [astro-ph.CO])
The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays. (arXiv:1211.4590v1 [astro-ph.CO]):
Recent observations of massive galaxies indicate that they double in mass and
quintuple in size between redshift z = 1 and the present, despite undergoing
very little star formation, suggesting that galaxy mergers drive the evolution.
Since these galaxies will contain supermassive black holes, this suggests a
larger black hole merger rate, and therefore a larger gravitational-wave
signal, than previously expected. We calculate the merger-driven evolution of
the mass function, and find that merger rates are 10 to 30 times higher and
gravitational waves are 3 to 5 times stronger than previously estimated, so
that the gravitational-wave signal may already be detectable with existing data
from pulsar timing arrays. We also provide an explanation for the disagreement
with past estimates that were based on dark matter halo simulations.
Recent observations of massive galaxies indicate that they double in mass and
quintuple in size between redshift z = 1 and the present, despite undergoing
very little star formation, suggesting that galaxy mergers drive the evolution.
Since these galaxies will contain supermassive black holes, this suggests a
larger black hole merger rate, and therefore a larger gravitational-wave
signal, than previously expected. We calculate the merger-driven evolution of
the mass function, and find that merger rates are 10 to 30 times higher and
gravitational waves are 3 to 5 times stronger than previously estimated, so
that the gravitational-wave signal may already be detectable with existing data
from pulsar timing arrays. We also provide an explanation for the disagreement
with past estimates that were based on dark matter halo simulations.
Jet Power and Black Hole Spin: Testing an Empirical Relationship and Using it to Predict the Spins of Six Black Holes. (arXiv:1211.5379v1 [astro-ph.HE])
Jet Power and Black Hole Spin: Testing an Empirical Relationship and Using it to Predict the Spins of Six Black Holes. (arXiv:1211.5379v1 [astro-ph.HE]):
Using 5 GHz radio luminosity at light-curve maximum as a proxy for jet power
and black-hole spin measurements obtained via the continuum-fitting method,
Narayan & McClintock (2012) presented the first direct evidence for a
relationship between jet power and black hole spin for four transient
black-hole binaries. We test and confirm their empirical relationship using a
fifth source, H1743-322, whose spin was recently measured. We show that this
relationship is consistent with Fe-line spin measurements provided that the
black hole spin axis is assumed to be aligned with the binary angular momentum
axis. We also show that, during a major outburst of a black hole transient, the
system reasonably approximates an X-ray standard candle. We further show, using
the standard synchrotron bubble model, that the radio luminosity at light-curve
maximum is a good proxy for jet kinetic energy. Thus, the observed tight
correlation between radio power and black hole spin indicates a strong
underlying link between mechanical jet power and black hole spin. Using the
fitted correlation between radio power and spin for the above five calibration
sources, we predict the spins of six other black holes in X-ray/radio transient
systems with low-mass companions. Remarkably, these predicted spins are all
relatively low, especially when compared to the high measured spins of black
holes in persistent, wind-fed systems with massive companions.
Using 5 GHz radio luminosity at light-curve maximum as a proxy for jet power
and black-hole spin measurements obtained via the continuum-fitting method,
Narayan & McClintock (2012) presented the first direct evidence for a
relationship between jet power and black hole spin for four transient
black-hole binaries. We test and confirm their empirical relationship using a
fifth source, H1743-322, whose spin was recently measured. We show that this
relationship is consistent with Fe-line spin measurements provided that the
black hole spin axis is assumed to be aligned with the binary angular momentum
axis. We also show that, during a major outburst of a black hole transient, the
system reasonably approximates an X-ray standard candle. We further show, using
the standard synchrotron bubble model, that the radio luminosity at light-curve
maximum is a good proxy for jet kinetic energy. Thus, the observed tight
correlation between radio power and black hole spin indicates a strong
underlying link between mechanical jet power and black hole spin. Using the
fitted correlation between radio power and spin for the above five calibration
sources, we predict the spins of six other black holes in X-ray/radio transient
systems with low-mass companions. Remarkably, these predicted spins are all
relatively low, especially when compared to the high measured spins of black
holes in persistent, wind-fed systems with massive companions.
Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey. (arXiv:1211.5140v1 [astro-ph.CO])
Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey. (arXiv:1211.5140v1 [astro-ph.CO]):
We place general constraints on the luminosity and mass of hot X-ray emitting
gas residing in extended "hot halos" around nearby massive galaxies. We examine
stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog
(2MVIG), as well as subsets of this sample based on galaxy morphology and
K-band luminosity. We detect X-ray emission at high confidence (ranging up to
nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc
is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the
early-type galaxies are more than twice as luminous as the late-type galaxies.
Using a spatial analysis, we also find evidence for extended emission around
five out of seven subsamples (the full sample, the luminous galaxies,
early-type galaxies, luminous late-type galaxies, and luminous early-type
galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively.
Several additional lines of evidence also support this conclusion and suggest
that about 1/2 of the total emission is extended, and about 1/3 of the extended
emission comes from hot gas. For the sample of luminous galaxies, which has the
strongest evidence for extended emission, the average hot gas mass is 4x10^9
Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.
We place general constraints on the luminosity and mass of hot X-ray emitting
gas residing in extended "hot halos" around nearby massive galaxies. We examine
stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog
(2MVIG), as well as subsets of this sample based on galaxy morphology and
K-band luminosity. We detect X-ray emission at high confidence (ranging up to
nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc
is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the
early-type galaxies are more than twice as luminous as the late-type galaxies.
Using a spatial analysis, we also find evidence for extended emission around
five out of seven subsamples (the full sample, the luminous galaxies,
early-type galaxies, luminous late-type galaxies, and luminous early-type
galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively.
Several additional lines of evidence also support this conclusion and suggest
that about 1/2 of the total emission is extended, and about 1/3 of the extended
emission comes from hot gas. For the sample of luminous galaxies, which has the
strongest evidence for extended emission, the average hot gas mass is 4x10^9
Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.
A comparative study of statistical models for nuclear equation of state of stellar matter. (arXiv:1211.5990v1 [nucl-th])
A comparative study of statistical models for nuclear equation of state of stellar matter. (arXiv:1211.5990v1 [nucl-th]):
We compare three different statistical models for the equation of state (EOS)
of stellar matter at subnuclear densities and temperatures (0.5-10 MeV)
expected to occur during the collapse of massive stars and supernova
explosions. The models introduce the distributions of various nuclear species
in nuclear statistical equilibrium, but use somewhat different nuclear physics
inputs. It is demonstrated that the basic thermodynamical quantities of stellar
matter under these conditions are similar, except in the region of high
densities and low temperatures. We demonstrate that mass and isotopic
distributions have considerable differences related to the different
assumptions of the models on properties of nuclei at these stellar conditions.
Overall, the three models give similar trends, but the details reflect the
uncertainties related to the modelling of medium effects, such as the
temperature and density dependence of surface and bulk energies of heavy
nuclei, and the nuclear shell structure effects. In order to establish a
relationship between nuclear physics inputs for astrophysical calculations and
the experimental data obtained from intermediate-energy nuclear reactions, we
also discuss the similarities and differences of the conditions reached during
supernova explosions and heavy-ion collisions.
Note: One of the few EOS papers to consider what the impact of variable EOS would have on other areas of astrophysics, as opposed to pure nuclear physics issues.
We compare three different statistical models for the equation of state (EOS)
of stellar matter at subnuclear densities and temperatures (0.5-10 MeV)
expected to occur during the collapse of massive stars and supernova
explosions. The models introduce the distributions of various nuclear species
in nuclear statistical equilibrium, but use somewhat different nuclear physics
inputs. It is demonstrated that the basic thermodynamical quantities of stellar
matter under these conditions are similar, except in the region of high
densities and low temperatures. We demonstrate that mass and isotopic
distributions have considerable differences related to the different
assumptions of the models on properties of nuclei at these stellar conditions.
Overall, the three models give similar trends, but the details reflect the
uncertainties related to the modelling of medium effects, such as the
temperature and density dependence of surface and bulk energies of heavy
nuclei, and the nuclear shell structure effects. In order to establish a
relationship between nuclear physics inputs for astrophysical calculations and
the experimental data obtained from intermediate-energy nuclear reactions, we
also discuss the similarities and differences of the conditions reached during
supernova explosions and heavy-ion collisions.
Note: One of the few EOS papers to consider what the impact of variable EOS would have on other areas of astrophysics, as opposed to pure nuclear physics issues.
Feedback from High-Mass X-Ray Binaries on the High Redshift Intergalactic Medium : Model Spectra. (arXiv:1211.5854v1 [astro-ph.CO])
Feedback from High-Mass X-Ray Binaries on the High Redshift Intergalactic Medium : Model Spectra. (arXiv:1211.5854v1 [astro-ph.CO]):
Massive stars at redshifts z > 6 are predicted to have played a pivotal role
in cosmological reionization as luminous sources of ultra-violet (UV) photons.
However, the remnants of these massive stars could be equally important as
X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the
absorption cross section of neutral hydrogen decreases sharply with photon
energy (proportional to the inverse cube), X-rays can escape more freely than
UV photons from the star-forming regions in which they are produced, allowing
HMXBs to make a potentially significant contribution to the ionizing X-ray
background during reionization. In this paper, we explore the ionizing power of
HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar
population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB
Cygnus X-1 as our template, we propose a composite HMXB spectral energy
distribution consisting of black-body and power-law components, whose
contributions depend on the accretion state of the system. We determine the
time-dependent ionizing power of a combined population of UV-luminous stars and
X-ray luminous HMXBs, and deduce fitting formulae for the boost in the
population's ionizing power arising from HMXBs; these fits allow for simple
implementation of HMXB feedback in numerical simulations. Based on this
analysis, we estimate the contribution of high redshift HMXBs to the
present-day soft X-ray background, and we show that it is a factor of ~100-1000
smaller than the observed limit. Finally, we discuss the implications of our
results for the role of HMXBs in reionization and in high redshift galaxy
formation.
Note: An interesting concept to consider feedback from non-SMBHs
Massive stars at redshifts z > 6 are predicted to have played a pivotal role
in cosmological reionization as luminous sources of ultra-violet (UV) photons.
However, the remnants of these massive stars could be equally important as
X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the
absorption cross section of neutral hydrogen decreases sharply with photon
energy (proportional to the inverse cube), X-rays can escape more freely than
UV photons from the star-forming regions in which they are produced, allowing
HMXBs to make a potentially significant contribution to the ionizing X-ray
background during reionization. In this paper, we explore the ionizing power of
HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar
population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB
Cygnus X-1 as our template, we propose a composite HMXB spectral energy
distribution consisting of black-body and power-law components, whose
contributions depend on the accretion state of the system. We determine the
time-dependent ionizing power of a combined population of UV-luminous stars and
X-ray luminous HMXBs, and deduce fitting formulae for the boost in the
population's ionizing power arising from HMXBs; these fits allow for simple
implementation of HMXB feedback in numerical simulations. Based on this
analysis, we estimate the contribution of high redshift HMXBs to the
present-day soft X-ray background, and we show that it is a factor of ~100-1000
smaller than the observed limit. Finally, we discuss the implications of our
results for the role of HMXBs in reionization and in high redshift galaxy
formation.
Note: An interesting concept to consider feedback from non-SMBHs
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