The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission. (arXiv:1301.7307v1 [astro-ph.IM]):
The Nuclear Spectroscopic Telescope Array (NuSTAR) mission, launched on 13
June 2012, is the first focusing high-energy X-ray telescope in orbit. NuSTAR
operates in the band from 3 -- 79 keV, extending the sensitivity of focusing
far beyond the ~10 keV high-energy cutoff achieved by all previous X-ray
satellites. The inherently low-background associated with concentrating the
X-ray light enables NuSTAR to probe the hard X-ray sky with a more than
one-hundred-fold improvement in sensitivity over the collimated or coded-mask
instruments that have operated in this bandpass. Using its unprecedented
combination of sensitivity, spatial and spectral resolution, NuSTAR will pursue
five primary scientific objectives, and will also undertake a broad program of
targeted observations. The observatory consists of two co-aligned
grazing-incidence X-ray telescopes pointed at celestial targets by a three-axis
stabilized spacecraft. Deployed into a 600 km, near-circular, 6degree
inclination orbit, the Observatory has now completed commissioning, and is
performing consistent with pre-launch expectations. NuSTAR is now executing its
primary science mission, and with an expected orbit lifetime of ten years, we
anticipate proposing a guest investigator program, to begin in Fall 2014.
Thursday, January 31, 2013
Ultra-fast outflows (aka UFOs) from AGNs and QSOs. (arXiv:1301.7199v1 [astro-ph.HE])
Ultra-fast outflows (aka UFOs) from AGNs and QSOs. (arXiv:1301.7199v1 [astro-ph.HE]):
During the last decade, strong observational evidence has been accumulated
for the existence of massive, high velocity winds/outflows (aka Ultra Fast
Outflows, UFOs) in nearby AGNs and in more distant quasars. Here we briefly
review some of the most recent developments in this field and discuss the
relevance of UFOs for both understanding the physics of accretion disk winds in
AGNs, and for quantifying the global amount of AGN feedback on the surrounding
medium.
During the last decade, strong observational evidence has been accumulated
for the existence of massive, high velocity winds/outflows (aka Ultra Fast
Outflows, UFOs) in nearby AGNs and in more distant quasars. Here we briefly
review some of the most recent developments in this field and discuss the
relevance of UFOs for both understanding the physics of accretion disk winds in
AGNs, and for quantifying the global amount of AGN feedback on the surrounding
medium.
A black-hole mass measurement from molecular gas kinematics in NGC4526. (arXiv:1301.7184v1 [astro-ph.CO])
A black-hole mass measurement from molecular gas kinematics in NGC4526. (arXiv:1301.7184v1 [astro-ph.CO]):
The masses of the supermassive black-holes found in galaxy bulges are
correlated with a multitude of galaxy properties, leading to suggestions that
galaxies and black-holes may evolve together. The number of reliably measured
black-hole masses is small, and the number of methods for measuring them is
limited, holding back attempts to understand this co-evolution. Directly
measuring black-hole masses is currently possible with stellar kinematics (in
early-type galaxies), ionised-gas kinematics (in some spiral and early-type
galaxies) and in rare objects which have central maser emission. Here we report
that by modelling the effect of a black-hole on the kinematics of molecular gas
it is possible to fit interferometric observations of CO emission and thereby
accurately estimate black hole masses. We study the dynamics of the gas in the
early-type galaxy NGC4526, and obtain a best fit which requires the presence of
a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit).
With next generation mm-interferometers (e.g. ALMA) these observations could be
reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing
time. The use of molecular gas as a kinematic tracer should thus allow one to
estimate black-hole masses in hundreds of galaxies in the local universe, many
more than accessible with current techniques.
The masses of the supermassive black-holes found in galaxy bulges are
correlated with a multitude of galaxy properties, leading to suggestions that
galaxies and black-holes may evolve together. The number of reliably measured
black-hole masses is small, and the number of methods for measuring them is
limited, holding back attempts to understand this co-evolution. Directly
measuring black-hole masses is currently possible with stellar kinematics (in
early-type galaxies), ionised-gas kinematics (in some spiral and early-type
galaxies) and in rare objects which have central maser emission. Here we report
that by modelling the effect of a black-hole on the kinematics of molecular gas
it is possible to fit interferometric observations of CO emission and thereby
accurately estimate black hole masses. We study the dynamics of the gas in the
early-type galaxy NGC4526, and obtain a best fit which requires the presence of
a central dark-object of 4.5(+4.2-3.0)x10^8 Msun (3 sigma confidence limit).
With next generation mm-interferometers (e.g. ALMA) these observations could be
reproduced in galaxies out to 75 megaparsecs in less the 5 hours of observing
time. The use of molecular gas as a kinematic tracer should thus allow one to
estimate black-hole masses in hundreds of galaxies in the local universe, many
more than accessible with current techniques.
Tuesday, January 29, 2013
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data. (arXiv:1301.6162v1 [astro-ph.CO])
Probing the Dawn of Galaxies at z~9-12: New Constraints from HUDF12/XDF and CANDELS Data. (arXiv:1301.6162v1 [astro-ph.CO]):
We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization.
We present a comprehensive analysis of z>8 galaxies based on ultra-deep
WFC3/IR data. We constrain the evolution of the UV luminosity function (LF) and
luminosity densities from z~11 to z~8 by exploiting all the WFC3/IR data over
the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in
addition to the HUDF09 parallel field data, as well as wider area WFC3/IR
imaging over GOODS-South. Galaxies are selected based on the Lyman Break
Technique in three samples centered around z~9, z~10 and z~11, with seven z~9
galaxy candidates, and one each at z~10 and z~11. We confirm a new z~10
candidate (with z=9.8+-0.6) that was not convincingly identified in our first
z~10 sample. The deeper data over the HUDF confirms all our previous z>~7.5
candidates as genuine high-redshift candidates, and extends our samples to
higher redshift and fainter limits (H_160~29.8 mag). We perform one of the
first estimates of the z~9 UV LF and improve our previous constraints at z~10.
Extrapolating the lower redshift UV LF evolution should have revealed 17 z~9
and 9 z~10 sources, i.e., a factor ~3x and 9x larger than observed. The
inferred star-formation rate density (SFRD) in galaxies above 0.7 M_sun/yr
decreases by 0.6+-0.2 dex from z~8 to z~9, in good agreement with previous
estimates. The low number of sources found at z>8 is consistent with a very
rapid build-up of galaxies across z~10 to z~8. From a combination of all
current measurements, we find a best estimate of a factor 10x decrease in the
SFRD from z~8 to z~10, following (1+z)^(-11.4+-3.1). Our measurements thus
confirm our previous finding of an accelerated evolution beyond z~8, and
signify a rapid build-up of galaxies with M_UV<-17.7 within only ~200 Myr from
z~10 to z~8, in the heart of cosmic reionization.
Wednesday, January 23, 2013
A link between measured neutron star masses and lattice QCD data. (arXiv:1212.5907v1 [astro-ph.SR])
A link between measured neutron star masses and lattice QCD data. (arXiv:1212.5907v1 [astro-ph.SR]):
We study the hadron-quark phase transition in neutron star matter and the
structural properties of hybrid stars using an equation of state (EOS) for the
quark phase derived with the Field Correlator Method (FCM). We make use of
measured neutron star masses, and particularly the mass of PSR J1614-2230, to
constrain the values of the gluon condensate $G_2$ which is one of the EOS
parameter within the FCM. We find that the values of $G_2$ extracted from the
mass measurement of PSR J1614-2230 are fully consistent with the values of the
same quantity derived, within the FCM, from recent lattice QCD calculations of
the deconfinement transition temperature at zero baryon chemical potential. The
FCM thus provides a powerful tool to link numerical calculations of QCD on a
space-time lattice with neutron stars physics.
We study the hadron-quark phase transition in neutron star matter and the
structural properties of hybrid stars using an equation of state (EOS) for the
quark phase derived with the Field Correlator Method (FCM). We make use of
measured neutron star masses, and particularly the mass of PSR J1614-2230, to
constrain the values of the gluon condensate $G_2$ which is one of the EOS
parameter within the FCM. We find that the values of $G_2$ extracted from the
mass measurement of PSR J1614-2230 are fully consistent with the values of the
same quantity derived, within the FCM, from recent lattice QCD calculations of
the deconfinement transition temperature at zero baryon chemical potential. The
FCM thus provides a powerful tool to link numerical calculations of QCD on a
space-time lattice with neutron stars physics.
What X-ray source counts can tell about the large scale matter distribution. (arXiv:1212.5891v1 [astro-ph.CO])
What X-ray source counts can tell about the large scale matter distribution. (arXiv:1212.5891v1 [astro-ph.CO]):
Sources generating most of the X-ray background (XRB) are dispersed over a
wide range of redshifts. Thus, statistical characteristics of the source
distribution carry the information on the matter distribution on very large
scales. We test the possibility to detect the variation of the X-ray source
number counts over the celestial sphere. A large number of Chandra pointings
spread over both galactic hemispheres is investigated. A search for all the
point-like sources in the soft band of 0.5 - 2 keV is performed, and
statistical assessment of the population of sources below the detection
threshold is carried out. A homogeneous sample of the number counts at fluxes
above ~10^{-16} erg/s/cm^2 for more than 300 ACIS fields was constructed. The
counts correlations between overlapping fields were used to assess the accuracy
of the computational methods used in the analysis. It is shown that the source
number counts vary between fields at the level only slightly larger than the
fluctuation amplitude expected for the random (Poissonian) distribution.
Nevertheless, small asymmetry between galactic hemispheres is present. The
average number of sources in the northern hemisphere is larger than in the
southern at the 2.75 sigma level. Also the autocorrelation function of the
source density in both hemispheres are substantially different. Possible
explanations for the observed anisotropies are considered. If the effect is
unrelated to the observational selection, a large scale inhomogeneities in the
distribution of X-ray sources are required. Correlations of the source number
counts observed in the southern hemisphere could be generated by a coherent
structure extending over 1200 Mpc.
Sources generating most of the X-ray background (XRB) are dispersed over a
wide range of redshifts. Thus, statistical characteristics of the source
distribution carry the information on the matter distribution on very large
scales. We test the possibility to detect the variation of the X-ray source
number counts over the celestial sphere. A large number of Chandra pointings
spread over both galactic hemispheres is investigated. A search for all the
point-like sources in the soft band of 0.5 - 2 keV is performed, and
statistical assessment of the population of sources below the detection
threshold is carried out. A homogeneous sample of the number counts at fluxes
above ~10^{-16} erg/s/cm^2 for more than 300 ACIS fields was constructed. The
counts correlations between overlapping fields were used to assess the accuracy
of the computational methods used in the analysis. It is shown that the source
number counts vary between fields at the level only slightly larger than the
fluctuation amplitude expected for the random (Poissonian) distribution.
Nevertheless, small asymmetry between galactic hemispheres is present. The
average number of sources in the northern hemisphere is larger than in the
southern at the 2.75 sigma level. Also the autocorrelation function of the
source density in both hemispheres are substantially different. Possible
explanations for the observed anisotropies are considered. If the effect is
unrelated to the observational selection, a large scale inhomogeneities in the
distribution of X-ray sources are required. Correlations of the source number
counts observed in the southern hemisphere could be generated by a coherent
structure extending over 1200 Mpc.
Super-spinning compact objects generated by thick accretion disks. (arXiv:1212.5848v1 [gr-qc])
Super-spinning compact objects generated by thick accretion disks. (arXiv:1212.5848v1 [gr-qc]):
If astrophysical black hole candidates are the Kerr black holes predicted by
General Relativity, the value of their spin parameter must be subject to the
{\it theoretical bound} $|a_*| \le 1$. In this work, we consider the
possibility that these objects are either non-Kerr black holes in an
alternative theory of gravity or exotic compact objects in General Relativity.
Such a possibility is not in contradiction with current data and it can be
tested with future observational facilities. We study the accretion process
when their accretion disk is geometrically thick with a simple version of the
Polish doughnut model. The picture of the accretion process may be
qualitatively different from the one around a Kerr black hole. The inner edge
of the accretion disk may not have the typical cusp on the equatorial plane any
more, but there may be two cusps, respectively above and below the equatorial
plane. We discuss the evolution of the spin parameter as a consequence of the
accretion process and we estimate the maximum value of the spin parameter of
these objects as a function of their deformation. Lastly, we compare our
results with the current estimates of the mean radiative efficiency of AGNs. We
find the observational bound $|a_*| \lesssim 1.3$ for the spin parameter of the
super-massive black hole candidates at the centers of galaxies, which we argue
to be almost independent of the exact nature of these objects.
If astrophysical black hole candidates are the Kerr black holes predicted by
General Relativity, the value of their spin parameter must be subject to the
{\it theoretical bound} $|a_*| \le 1$. In this work, we consider the
possibility that these objects are either non-Kerr black holes in an
alternative theory of gravity or exotic compact objects in General Relativity.
Such a possibility is not in contradiction with current data and it can be
tested with future observational facilities. We study the accretion process
when their accretion disk is geometrically thick with a simple version of the
Polish doughnut model. The picture of the accretion process may be
qualitatively different from the one around a Kerr black hole. The inner edge
of the accretion disk may not have the typical cusp on the equatorial plane any
more, but there may be two cusps, respectively above and below the equatorial
plane. We discuss the evolution of the spin parameter as a consequence of the
accretion process and we estimate the maximum value of the spin parameter of
these objects as a function of their deformation. Lastly, we compare our
results with the current estimates of the mean radiative efficiency of AGNs. We
find the observational bound $|a_*| \lesssim 1.3$ for the spin parameter of the
super-massive black hole candidates at the centers of galaxies, which we argue
to be almost independent of the exact nature of these objects.
The relationship between X-ray emission and accretion in X-ray selected AGNs. (arXiv:1212.5693v1 [astro-ph.HE])
The relationship between X-ray emission and accretion in X-ray selected AGNs. (arXiv:1212.5693v1 [astro-ph.HE]):
We study the link between the X-ray emission in radio-quiet AGNs and the
accretion rate on the central Supermassive Black-Hole (SMBH) using a
well-defined and statistically complete sample of 70 type1 AGNs extracted from
the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and
quantify the statistical correlations between the main parameters that
characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray
loudness), and the accretion rate, both absolute and relative to the Eddington
limit (Eddington ratio). Here, we summarize and discuss the main statistical
correlations found and their possible implications on current disk-corona
models.
We study the link between the X-ray emission in radio-quiet AGNs and the
accretion rate on the central Supermassive Black-Hole (SMBH) using a
well-defined and statistically complete sample of 70 type1 AGNs extracted from
the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and
quantify the statistical correlations between the main parameters that
characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray
loudness), and the accretion rate, both absolute and relative to the Eddington
limit (Eddington ratio). Here, we summarize and discuss the main statistical
correlations found and their possible implications on current disk-corona
models.
Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO])
Characterizing the Circumgalactic Medium of Nearby Galaxies with HST/COS and HST/STIS Absorption-Line Spectroscopy. (arXiv:1212.5658v1 [astro-ph.CO]):
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using
UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble
Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous
absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph.
CGM warm cloud properties are derived, including volume filling factors of
3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and
metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5
virial radii are metal-bearing and many have velocities consistent with being
bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass
in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total
baryons in massive spirals and comparable to the baryons in their parent galaxy
disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs
(<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon
fraction), suggesting that many of their warm clouds escape. Constant warm
cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3}
K) support the inference that previous COS detections of broad, shallow O VI
and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K)
intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM
clouds cannot account for all the "missing baryons" in spirals, the hot
intra-group gas can, and could account for ~20% of the cosmic baryon census at
z ~ 0 if this hot gas is ubiquitous among spiral groups.
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using
UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble
Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous
absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph.
CGM warm cloud properties are derived, including volume filling factors of
3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and
metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5
virial radii are metal-bearing and many have velocities consistent with being
bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass
in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total
baryons in massive spirals and comparable to the baryons in their parent galaxy
disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs
(<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon
fraction), suggesting that many of their warm clouds escape. Constant warm
cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3}
K) support the inference that previous COS detections of broad, shallow O VI
and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K)
intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM
clouds cannot account for all the "missing baryons" in spirals, the hot
intra-group gas can, and could account for ~20% of the cosmic baryon census at
z ~ 0 if this hot gas is ubiquitous among spiral groups.
Galaxy Formation: Where Do We Stand?. (arXiv:1212.5641v1 [astro-ph.CO])
Galaxy Formation: Where Do We Stand?. (arXiv:1212.5641v1 [astro-ph.CO]):
This paper presents a review of the topic of galaxy formation and evolution,
focusing on basic features of galaxies, and how these observables reveal how
galaxies and their stars assemble over cosmic time. I give an overview of the
observed properties of galaxies in the nearby universe and for those at higher
redshifts up to z~10. This includes a discussion of the major processes in
which galaxies assemble and how we can now observe these - including the merger
history of galaxies, the gas accretion and star formation rates. I show that
for the most massive galaxies mergers and accretion are about equally important
in the galaxy formation process between z = 1-3, while this likely differs for
lower mass systems. I also discuss the mass differential evolution for
galaxies, as well as how environment can affect galaxy evolution, although mass
is the primary criteria for driving evolution. I also discuss how we are
beginning to measure the dark matter content of galaxies at different epochs as
measured through kinematics and clustering. Finally, I review how observables
of galaxies, and the observed galaxy formation process, compares with
predictions from simulations of galaxy formation, finding significant
discrepancies in the abundances of massive galaxies and the merger history. I
conclude by examining prospects for the future using JWST, Euclid, SKA, and the
ELTs in addressing outstanding issues.
This paper presents a review of the topic of galaxy formation and evolution,
focusing on basic features of galaxies, and how these observables reveal how
galaxies and their stars assemble over cosmic time. I give an overview of the
observed properties of galaxies in the nearby universe and for those at higher
redshifts up to z~10. This includes a discussion of the major processes in
which galaxies assemble and how we can now observe these - including the merger
history of galaxies, the gas accretion and star formation rates. I show that
for the most massive galaxies mergers and accretion are about equally important
in the galaxy formation process between z = 1-3, while this likely differs for
lower mass systems. I also discuss the mass differential evolution for
galaxies, as well as how environment can affect galaxy evolution, although mass
is the primary criteria for driving evolution. I also discuss how we are
beginning to measure the dark matter content of galaxies at different epochs as
measured through kinematics and clustering. Finally, I review how observables
of galaxies, and the observed galaxy formation process, compares with
predictions from simulations of galaxy formation, finding significant
discrepancies in the abundances of massive galaxies and the merger history. I
conclude by examining prospects for the future using JWST, Euclid, SKA, and the
ELTs in addressing outstanding issues.
Hadron-Quark Crossover and Massive Hybrid Stars. (arXiv:1212.6803v1 [nucl-th])
Hadron-Quark Crossover and Massive Hybrid Stars. (arXiv:1212.6803v1 [nucl-th]):
On the basis of the percolation picture from the hadronic phase with hyperons
to the quark phase with strangeness, we construct a new equation of state (EOS)
with the pressure interpolated as a function of the baryon density. The maximum
mass of neutron stars can exceed $2M_{\odot}$ if the following two conditions
are satisfied; (i) the crossover from the hadronic matter to the quark matter
takes place at around three times the normal nuclear matter density, and (ii)
the quark matter is strongly interacting in the crossover region. This is in
contrast to the conventional approach assuming the first order phase transition
in which the EOS becomes always soft due to the presence of the quark matter at
high density. Although the choice of the hadronic EOS does not affect the above
conclusion on the maximum mass, the three-body force among nucleons and
hyperons plays an essential role for the onset of the hyperon mixing and the
cooling of neutron stars.
On the basis of the percolation picture from the hadronic phase with hyperons
to the quark phase with strangeness, we construct a new equation of state (EOS)
with the pressure interpolated as a function of the baryon density. The maximum
mass of neutron stars can exceed $2M_{\odot}$ if the following two conditions
are satisfied; (i) the crossover from the hadronic matter to the quark matter
takes place at around three times the normal nuclear matter density, and (ii)
the quark matter is strongly interacting in the crossover region. This is in
contrast to the conventional approach assuming the first order phase transition
in which the EOS becomes always soft due to the presence of the quark matter at
high density. Although the choice of the hadronic EOS does not affect the above
conclusion on the maximum mass, the three-body force among nucleons and
hyperons plays an essential role for the onset of the hyperon mixing and the
cooling of neutron stars.
Review of Multi-messenger observations of neutron rich matter. (arXiv:1212.6405v1 [nucl-th])
Review of Multi-messenger observations of neutron rich matter. (arXiv:1212.6405v1 [nucl-th]):
At very high densities, electrons react with protons to form neutron rich
matter. This material is central to many fundamental questions in nuclear
physics and astrophysics. Moreover, neutron rich matter is being studied with
an extraordinary variety of new tools such as the Facility for Rare Isotope
Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory
(LIGO). We describe the Lead Radius Experiment (PREX) that uses parity
violating electron scattering to measure the neutron radius of 208Pb. This has
important implications for neutron stars and their crusts. We discuss X-ray
observations of neutron star radii. These also have important implications for
neutron rich matter. Gravitational waves (GW) open a new window on neutron rich
matter. They come from sources such as neutron star mergers, rotating neutron
star mountains, and collective r-mode oscillations. Using large scale molecular
dynamics simulations, we find neutron star crust to be very strong. It can
support mountains on rotating neutron stars large enough to generate detectable
gravitational waves. Finally, neutrinos from core collapse supernovae (SN)
provide another, qualitatively different probe of neutron rich matter.
Neutrinos escape from the surface of last scattering known as the
neutrino-sphere. This is a low density warm gas of neutron rich matter.
Neutrino-sphere conditions can be simulated in the laboratory with heavy ion
collisions. Observations of neutrinos can probe nucleosyntheses in SN. We
believe that combing astronomical observations using photons, GW, and
neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and
radioactive beams will fundamentally advance our knowledge of compact objects
in the heavens, the dense phases of QCD, the origin of the elements, and of
neutron rich matter.
At very high densities, electrons react with protons to form neutron rich
matter. This material is central to many fundamental questions in nuclear
physics and astrophysics. Moreover, neutron rich matter is being studied with
an extraordinary variety of new tools such as the Facility for Rare Isotope
Beams (FRIB) and the Laser Interferometer Gravitational Wave Observatory
(LIGO). We describe the Lead Radius Experiment (PREX) that uses parity
violating electron scattering to measure the neutron radius of 208Pb. This has
important implications for neutron stars and their crusts. We discuss X-ray
observations of neutron star radii. These also have important implications for
neutron rich matter. Gravitational waves (GW) open a new window on neutron rich
matter. They come from sources such as neutron star mergers, rotating neutron
star mountains, and collective r-mode oscillations. Using large scale molecular
dynamics simulations, we find neutron star crust to be very strong. It can
support mountains on rotating neutron stars large enough to generate detectable
gravitational waves. Finally, neutrinos from core collapse supernovae (SN)
provide another, qualitatively different probe of neutron rich matter.
Neutrinos escape from the surface of last scattering known as the
neutrino-sphere. This is a low density warm gas of neutron rich matter.
Neutrino-sphere conditions can be simulated in the laboratory with heavy ion
collisions. Observations of neutrinos can probe nucleosyntheses in SN. We
believe that combing astronomical observations using photons, GW, and
neutrinos, with laboratory experiments on nuclei, heavy ion collisions, and
radioactive beams will fundamentally advance our knowledge of compact objects
in the heavens, the dense phases of QCD, the origin of the elements, and of
neutron rich matter.
Hyperons and Condensed Kaons in Compact Stars. (arXiv:1301.0067v1 [nucl-th])
Hyperons and Condensed Kaons in Compact Stars. (arXiv:1301.0067v1 [nucl-th]):
Using the Callan-Klebanov bound state model for hyperons simulated on crystal
lattice to describe strange baryonic matter, we argue that to ${\cal O} (1)$ in
the large $N_c$ counting to which the theory is robust, hyperons can figure
only when -- or after -- kaons condense in compact-star matter. We also discuss
how the skyrmion-half-skyrmion topological transition affects the equation of
state (EoS) of dense baryonic matter. The observations made in this note open
wide the issue of how to theoretically access the EoS of compact stars.
Using the Callan-Klebanov bound state model for hyperons simulated on crystal
lattice to describe strange baryonic matter, we argue that to ${\cal O} (1)$ in
the large $N_c$ counting to which the theory is robust, hyperons can figure
only when -- or after -- kaons condense in compact-star matter. We also discuss
how the skyrmion-half-skyrmion topological transition affects the equation of
state (EoS) of dense baryonic matter. The observations made in this note open
wide the issue of how to theoretically access the EoS of compact stars.
Relative velocity of dark matter and barions in clusters of galaxies and measurements of their peculiar velocities. (arXiv:1301.0024v1 [astro-ph.CO])
Relative velocity of dark matter and barions in clusters of galaxies and measurements of their peculiar velocities. (arXiv:1301.0024v1 [astro-ph.CO]):
The increasing sensitivity of current experiments, which nowadays routinely
measure the thermal SZ effect within galaxy clusters, provide the hope that
peculiar velocities of individual clusters of galaxies will be measured rather
soon using the kinematic SZ effect. Also next generation of X-ray telescopes
with microcalorimeters, promise first detections of the motion of the intra
cluster medium (ICM) within clusters. We used a large set of cosmological,
hydrodynamical simulations, which cover very large cosmological volume, hosting
a large number of rich clusters of galaxies, as well as moderate volumes where
the internal structures of individual galaxy clusters can be resolved with very
high resolution to investigate, how the presence of baryons and their
associated physical processes like cooling and star-formation are affecting the
systematic difference between mass averaged velocities of dark matter and the
ICM inside a cluster. We, for the first time, quantify the peculiar motion of
galaxy clusters as function of the large scale environment. We also demonstrate
that especially in very massive systems, the relative velocity of the ICM
compared to the cluster peculiar velocity add significant scatter onto the
inferred peculiar velocity, especially when measurements are limited to the
central regions of the cluster. Depending on the aperture used, this scatter
varies between 50% and 20%, when going from the core (e.g. ten percent of the
virial radius) to the full cluster (e.g. the virial radius).
The increasing sensitivity of current experiments, which nowadays routinely
measure the thermal SZ effect within galaxy clusters, provide the hope that
peculiar velocities of individual clusters of galaxies will be measured rather
soon using the kinematic SZ effect. Also next generation of X-ray telescopes
with microcalorimeters, promise first detections of the motion of the intra
cluster medium (ICM) within clusters. We used a large set of cosmological,
hydrodynamical simulations, which cover very large cosmological volume, hosting
a large number of rich clusters of galaxies, as well as moderate volumes where
the internal structures of individual galaxy clusters can be resolved with very
high resolution to investigate, how the presence of baryons and their
associated physical processes like cooling and star-formation are affecting the
systematic difference between mass averaged velocities of dark matter and the
ICM inside a cluster. We, for the first time, quantify the peculiar motion of
galaxy clusters as function of the large scale environment. We also demonstrate
that especially in very massive systems, the relative velocity of the ICM
compared to the cluster peculiar velocity add significant scatter onto the
inferred peculiar velocity, especially when measurements are limited to the
central regions of the cluster. Depending on the aperture used, this scatter
varies between 50% and 20%, when going from the core (e.g. ten percent of the
virial radius) to the full cluster (e.g. the virial radius).
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data. (arXiv:1301.0816v1 [astro-ph.CO])
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data. (arXiv:1301.0816v1 [astro-ph.CO]):
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to break the
degeneracy between the cluster extent (R_500) and the integrated Compton
parameter (Y_500). The UPP scalings are found to be nearly identical to an
adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
complete, high signal to noise ratio subsample of 15 ACT clusters is used to
obtain cosmological constraints. We first confirm that constraints from SZ data
are limited by uncertainty in the scaling relation parameters rather than
sample size or measurement uncertainty. We next add in seven clusters from the
ACT Southern survey, including their dynamical mass measurements based on
galaxy velocity dispersions. In combination with WMAP7 these data
simultaneously constrain the scaling relation and cosmological parameters,
yielding \sigma_8 = 0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results
include marginalization over a 15% bias in dynamical mass relative to the true
halo mass. In an extension to LCDM that incorporates non-zero neutrino mass
density, we combine our data with WMAP7+BAO+Hubble constant measurements to
constrain \Sigma m_\nu < 0.29 eV (95% C. L.).
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to break the
degeneracy between the cluster extent (R_500) and the integrated Compton
parameter (Y_500). The UPP scalings are found to be nearly identical to an
adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
complete, high signal to noise ratio subsample of 15 ACT clusters is used to
obtain cosmological constraints. We first confirm that constraints from SZ data
are limited by uncertainty in the scaling relation parameters rather than
sample size or measurement uncertainty. We next add in seven clusters from the
ACT Southern survey, including their dynamical mass measurements based on
galaxy velocity dispersions. In combination with WMAP7 these data
simultaneously constrain the scaling relation and cosmological parameters,
yielding \sigma_8 = 0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results
include marginalization over a 15% bias in dynamical mass relative to the true
halo mass. In an extension to LCDM that incorporates non-zero neutrino mass
density, we combine our data with WMAP7+BAO+Hubble constant measurements to
constrain \Sigma m_\nu < 0.29 eV (95% C. L.).
Metal-mass-to-light ratios of the Perseus cluster out to the virial radius. (arXiv:1301.0655v1 [astro-ph.CO])
Metal-mass-to-light ratios of the Perseus cluster out to the virial radius. (arXiv:1301.0655v1 [astro-ph.CO]):
We analyzed XMM-Newton data of the Perseus cluster out to $\sim$1 Mpc, or
approximately half the virial radius. Using the flux ratios of Lyalpha lines of
H-like Si and S to Kalpha line of He-like Fe, the abundance ratios of Si/Fe and
S/Fe of the intracluster medium (ICM) were derived using the APEC plasma code
v2.0.1. The temperature dependence of the line ratio limits the systematic
uncertainty in the derived abundance ratio. The Si/Fe and S/Fe in the ICM of
the Perseus cluster show no radial gradient. The emission-weighted averages of
the Si/Fe and S/Fe ratios outside the cool core are 0.91 +- 0.08 and 0.93 +-
0.10, respectively, in solar units according to the solar abundance table of
Lodders (2003). These ratios indicate that most Fe was synthesized by
supernovae Ia. We collected K-band luminosities of galaxies and calculated the
ratio of Fe and Si mass in the ICM to K-band luminosity, iron-mass-to-light
ratio (IMLR) and silicon-mass-to-light ratio (SMLR). Within $\sim$1 Mpc, the
cumulative IMLR and SMLR increase with radius. Using Suzaku data for the
northwest and east directions, we also calculated the IMLR out to $\sim$ 1.8
Mpc, or about the virial radius. We constrained the SMLR out to this radius and
discussed the slope of the initial mass function of stars in the cluster. Using
the cumulative IMLR profile, we discuss the past supernova Ia rate.
We analyzed XMM-Newton data of the Perseus cluster out to $\sim$1 Mpc, or
approximately half the virial radius. Using the flux ratios of Lyalpha lines of
H-like Si and S to Kalpha line of He-like Fe, the abundance ratios of Si/Fe and
S/Fe of the intracluster medium (ICM) were derived using the APEC plasma code
v2.0.1. The temperature dependence of the line ratio limits the systematic
uncertainty in the derived abundance ratio. The Si/Fe and S/Fe in the ICM of
the Perseus cluster show no radial gradient. The emission-weighted averages of
the Si/Fe and S/Fe ratios outside the cool core are 0.91 +- 0.08 and 0.93 +-
0.10, respectively, in solar units according to the solar abundance table of
Lodders (2003). These ratios indicate that most Fe was synthesized by
supernovae Ia. We collected K-band luminosities of galaxies and calculated the
ratio of Fe and Si mass in the ICM to K-band luminosity, iron-mass-to-light
ratio (IMLR) and silicon-mass-to-light ratio (SMLR). Within $\sim$1 Mpc, the
cumulative IMLR and SMLR increase with radius. Using Suzaku data for the
northwest and east directions, we also calculated the IMLR out to $\sim$ 1.8
Mpc, or about the virial radius. We constrained the SMLR out to this radius and
discussed the slope of the initial mass function of stars in the cluster. Using
the cumulative IMLR profile, we discuss the past supernova Ia rate.
Fast variability as a probe of the smallest regions around accreting black holes. (arXiv:1301.0627v1 [astro-ph.HE])
Fast variability as a probe of the smallest regions around accreting black holes. (arXiv:1301.0627v1 [astro-ph.HE]):
We extract the spectra of the fastest variability (above 10 Hz) from the
black hole XTE J1550-564 during a transition from hard to soft state on the
rise to outburst. We confirm previous results that the rapid variability
contains no significant disc component despite this being strongly present in
the total spectrum of the softer observations. We model ionised reflection
significantly better than previous work, and show that this is also suppressed
in the rapid variability spectrum compared to the total emission. This is
consistent with the fast variability having its origin in a hot inner flow
close to the black hole rather than in the accretion disc or in a corona above
it. However, the rapid variability spectrum is not simply the same as the total
Comptonised emission. It is always significantly harder, by an amount which
increases as the spectrum softens during the outburst. This adds to evidence
from time lags that the Comptonisation region is inhomogeneous, with harder
spectra produced closest to the black hole, the same region which produces the
fastest variability.
We extract the spectra of the fastest variability (above 10 Hz) from the
black hole XTE J1550-564 during a transition from hard to soft state on the
rise to outburst. We confirm previous results that the rapid variability
contains no significant disc component despite this being strongly present in
the total spectrum of the softer observations. We model ionised reflection
significantly better than previous work, and show that this is also suppressed
in the rapid variability spectrum compared to the total emission. This is
consistent with the fast variability having its origin in a hot inner flow
close to the black hole rather than in the accretion disc or in a corona above
it. However, the rapid variability spectrum is not simply the same as the total
Comptonised emission. It is always significantly harder, by an amount which
increases as the spectrum softens during the outburst. This adds to evidence
from time lags that the Comptonisation region is inhomogeneous, with harder
spectra produced closest to the black hole, the same region which produces the
fastest variability.
The X-ray/SZ view of the virial region. II. Gas mass fraction. (arXiv:1301.0624v1 [astro-ph.CO])
The X-ray/SZ view of the virial region. II. Gas mass fraction. (arXiv:1301.0624v1 [astro-ph.CO]):
Several recent studies used the hot gas fraction of galaxy clusters as a
standard ruler to constrain dark energy, which provides competitive results
compared to other techniques. This method, however, relies on the assumption
that the baryon fraction in clusters agrees with the cosmic value
Omega_b/Omega_m, and does not differ from one system to another. We test this
hypothesis by measuring the gas mass fraction over the entire cluster volume in
a sample of local clusters. Combining the SZ thermal pressure from Planck and
the X-ray gas density from ROSAT, we measured for the first time the average
gas fraction (fgas) out to the virial radius and beyond in a large sample of
clusters. We also obtained azimuthally-averaged measurements of the gas
fraction for 18 individual systems, which we used to compute the scatter of
fgas around the mean value at different radii and its dependence on the
cluster's temperature. The gas mass fraction increases with radius and reaches
the cosmic baryon fraction close to R200. At R200, we measure
fgas,200=0.176+/-0.009. We find significant differences between the baryon
fraction of relaxed, cool-core (CC) systems and unrelaxed, non-cool core (NCC)
clusters in the outer regions. In average, the gas fraction in NCC clusters
slightly exceeds the cosmic baryon fraction, while in CC systems the gas
fraction converges to the expected value when accounting for the stellar
content, without any evidence for variations from one system to another. We
find that fgas estimates in NCC systems slightly disagree with the cosmic value
approaching R200. This result could be explained either by a violation of the
assumption of hydrostatic equilibrium or by an inhomogeneous distribution of
the gas mass. Conversely, cool-core clusters are found to provide reliable
constraints on fgas at overdensities >200, which makes them suitable for
cosmological studies.
Several recent studies used the hot gas fraction of galaxy clusters as a
standard ruler to constrain dark energy, which provides competitive results
compared to other techniques. This method, however, relies on the assumption
that the baryon fraction in clusters agrees with the cosmic value
Omega_b/Omega_m, and does not differ from one system to another. We test this
hypothesis by measuring the gas mass fraction over the entire cluster volume in
a sample of local clusters. Combining the SZ thermal pressure from Planck and
the X-ray gas density from ROSAT, we measured for the first time the average
gas fraction (fgas) out to the virial radius and beyond in a large sample of
clusters. We also obtained azimuthally-averaged measurements of the gas
fraction for 18 individual systems, which we used to compute the scatter of
fgas around the mean value at different radii and its dependence on the
cluster's temperature. The gas mass fraction increases with radius and reaches
the cosmic baryon fraction close to R200. At R200, we measure
fgas,200=0.176+/-0.009. We find significant differences between the baryon
fraction of relaxed, cool-core (CC) systems and unrelaxed, non-cool core (NCC)
clusters in the outer regions. In average, the gas fraction in NCC clusters
slightly exceeds the cosmic baryon fraction, while in CC systems the gas
fraction converges to the expected value when accounting for the stellar
content, without any evidence for variations from one system to another. We
find that fgas estimates in NCC systems slightly disagree with the cosmic value
approaching R200. This result could be explained either by a violation of the
assumption of hydrostatic equilibrium or by an inhomogeneous distribution of
the gas mass. Conversely, cool-core clusters are found to provide reliable
constraints on fgas at overdensities >200, which makes them suitable for
cosmological studies.
The X-ray/SZ view of the virial region. I. Thermodynamic properties. (arXiv:1301.0617v1 [astro-ph.CO])
The X-ray/SZ view of the virial region. I. Thermodynamic properties. (arXiv:1301.0617v1 [astro-ph.CO]):
We measure the thermodynamic properties of cluster outer regions to provide
constraints on the processes that rule the formation of large scale structures.
We derived the thermodynamic properties of the intracluster gas (temperature,
entropy) by combining the SZ thermal pressure from Planck and the X-ray gas
density from ROSAT. This method allowed us to reconstruct for the first time
temperature and entropy profiles out to the virial radius and beyond in a large
sample of objects. At variance with several recent Suzaku studies, we find that
the entropy rises steadily with radius, albeit at at a somewhat lower rate than
predicted by self-similar expectations. We note significant differences between
relaxed, cool-core systems and unrelaxed clusters in the outer regions. Relaxed
systems appear to follow the self-similar expectations more closely than
perturbed objects. Our results indicate that the well-known entropy excess
observed in cluster cores extends well beyond the central regions. When
correcting for the gas depletion, the observed entropy profiles agree with the
prediction from gravitational collapse only, especially for cool-core clusters.
We measure the thermodynamic properties of cluster outer regions to provide
constraints on the processes that rule the formation of large scale structures.
We derived the thermodynamic properties of the intracluster gas (temperature,
entropy) by combining the SZ thermal pressure from Planck and the X-ray gas
density from ROSAT. This method allowed us to reconstruct for the first time
temperature and entropy profiles out to the virial radius and beyond in a large
sample of objects. At variance with several recent Suzaku studies, we find that
the entropy rises steadily with radius, albeit at at a somewhat lower rate than
predicted by self-similar expectations. We note significant differences between
relaxed, cool-core systems and unrelaxed clusters in the outer regions. Relaxed
systems appear to follow the self-similar expectations more closely than
perturbed objects. Our results indicate that the well-known entropy excess
observed in cluster cores extends well beyond the central regions. When
correcting for the gas depletion, the observed entropy profiles agree with the
prediction from gravitational collapse only, especially for cool-core clusters.
The interplay between X-ray photoevaporation and planet formation. (arXiv:1301.3015v1 [astro-ph.SR])
The interplay between X-ray photoevaporation and planet formation. (arXiv:1301.3015v1 [astro-ph.SR]):
We assess the potential of planet formation instigating the early formation
of a photoevaporation driven gap, up to radii larger than typical for
photoevaporation alone. For our investigation we make use of hydrodynamics
models of photoevaporating discs with a giant planet embedded. We find that, by
reducing the mass accretion flow onto the star, discs that form giant planets
will be dispersed at earlier times than discs without planets by X-ray
photoevaporation. By clearing the portion of the disc inner of the planet
orbital radius, planet formation induced photoevaporation (PIPE) is able to
produce transition disc that for a given mass accretion rate have larger holes
when compared to standard X-ray photoevaporation. This constitutes a possible
route for the formation of the observed class of accreting transition discs
with large holes, which are otherwise difficult to explain by planet formation
or photoevaporation alone. Moreover, assuming that a planet is able to filter
dust completely, PIPE produces a transition disc with a large hole and may
provide a mechanism to quickly shut down accretion. This process appears to be
too slow however to explain the observed desert in the population of transition
disc with large holes and low mass accretion rates.
We assess the potential of planet formation instigating the early formation
of a photoevaporation driven gap, up to radii larger than typical for
photoevaporation alone. For our investigation we make use of hydrodynamics
models of photoevaporating discs with a giant planet embedded. We find that, by
reducing the mass accretion flow onto the star, discs that form giant planets
will be dispersed at earlier times than discs without planets by X-ray
photoevaporation. By clearing the portion of the disc inner of the planet
orbital radius, planet formation induced photoevaporation (PIPE) is able to
produce transition disc that for a given mass accretion rate have larger holes
when compared to standard X-ray photoevaporation. This constitutes a possible
route for the formation of the observed class of accreting transition discs
with large holes, which are otherwise difficult to explain by planet formation
or photoevaporation alone. Moreover, assuming that a planet is able to filter
dust completely, PIPE produces a transition disc with a large hole and may
provide a mechanism to quickly shut down accretion. This process appears to be
too slow however to explain the observed desert in the population of transition
disc with large holes and low mass accretion rates.
Investigation of X-ray cavities in the cooling flow system Abell 1991. (arXiv:1301.2928v1 [astro-ph.CO])
Investigation of X-ray cavities in the cooling flow system Abell 1991. (arXiv:1301.2928v1 [astro-ph.CO]):
We present results based on the systematic analysis of \textit{Chandra}
archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991
with an objective to investigate properties of the X-ray cavities hosted by
this system. The unsharp masked image as well as 2-d $\beta$ model subtracted
residual image of Abell 1991 reveals a pair of X-ray cavities and a region of
excess emission in the central $\sim$12 kpc region. Both the cavities are of
ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray
surface brightness compared to that in the undisturbed regions. Spectral
analysis of X-ray photons extracted from the cavities lead to the temperature
values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and
$1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray
emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial
temperature profile derived for Abell 1991 reveals a positive temperature
gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines
in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec
region of Abell 1991 reveals relatively cooler three different knot like
features that are about 10\arcsec off the X-ray peak of the cluster. Total
power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum,
while the X-ray luminosity within the cooling radius is found to be 6.04
$\times 10^{43}$ \lum, comparison of which imply that the mechanical energy
released by the central AGN outburst is sufficient to balance the radiative
loss.
We present results based on the systematic analysis of \textit{Chandra}
archive data on the X-ray bright Abell Richness class-I type cluster Abell 1991
with an objective to investigate properties of the X-ray cavities hosted by
this system. The unsharp masked image as well as 2-d $\beta$ model subtracted
residual image of Abell 1991 reveals a pair of X-ray cavities and a region of
excess emission in the central $\sim$12 kpc region. Both the cavities are of
ellipsoidal shape and exhibit an order of magnitude deficiency in the X-ray
surface brightness compared to that in the undisturbed regions. Spectral
analysis of X-ray photons extracted from the cavities lead to the temperature
values equal to $1.77_{-0.12}^{+0.19}$ keV for N-cavity and
$1.53_{-0.06}^{+0.05}$ keV for S-cavity, while that for the excess X-ray
emission region is found to be equal to $2.06_{-0.07}^{+0.12}$ keV. Radial
temperature profile derived for Abell 1991 reveals a positive temperature
gradient, reaching to a maximum of 2.63 keV at $\sim$ 76 kpc and then declines
in outward direction. 0.5$-$2.0 keV soft band image of the central 15\arcsec
region of Abell 1991 reveals relatively cooler three different knot like
features that are about 10\arcsec off the X-ray peak of the cluster. Total
power of the cavities is found to be equal to $\sim 8.64\times 10^{43}$ \lum,
while the X-ray luminosity within the cooling radius is found to be 6.04
$\times 10^{43}$ \lum, comparison of which imply that the mechanical energy
released by the central AGN outburst is sufficient to balance the radiative
loss.
The Fractional Ionization of the Warm Neutral Interstellar Medium. (arXiv:1301.3144v1 [astro-ph.GA])
The Fractional Ionization of the Warm Neutral Interstellar Medium. (arXiv:1301.3144v1 [astro-ph.GA]):
When the neutral interstellar medium is exposed to EUV and soft X ray
radiation, the argon atoms in it are far more susceptible to being ionized than
the hydrogen atoms. We make use of this fact to determine the level of
ionization in the nearby, warm, neutral medium (WNM). By analyzing FUSE
observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred pc
away from the Sun, we can compare column densities of Ar I to those of O I,
where the relative ionization of oxygen can be used as a proxy for that of
hydrogen. The measured deficiency [ Ar I/O I]= 0.427+/- 0.11dex below the
expectation for a fully neutral medium implies that the electron density n(e)
\sim 0.04cm^- 3 if n(H)=0.5cm^- 3. This amount of ionization is considerably
larger than what we expect from primary photoionizations resulting from cosmic
rays, the diffuse X-ray background, and X-ray emitting sources within the
medium, along with the additional ionizations caused by energetic secondary
photoelectrons, Auger electrons, and photons from helium recombinations. We
favor an explanation that bursts of radiation created by previous, nearby
supernova remnants that have faded by now may have elevated the ionization, and
the gas has not yet recombined to a quiescent level. A different alternative is
that the low energy portion of the soft X ray background is poorly shielded by
the H I because it is frothy and has internal pockets of very hot, X-ray
emitting gases.
When the neutral interstellar medium is exposed to EUV and soft X ray
radiation, the argon atoms in it are far more susceptible to being ionized than
the hydrogen atoms. We make use of this fact to determine the level of
ionization in the nearby, warm, neutral medium (WNM). By analyzing FUSE
observations of ultraviolet spectra of 44 hot subdwarf stars a few hundred pc
away from the Sun, we can compare column densities of Ar I to those of O I,
where the relative ionization of oxygen can be used as a proxy for that of
hydrogen. The measured deficiency [ Ar I/O I]= 0.427+/- 0.11dex below the
expectation for a fully neutral medium implies that the electron density n(e)
\sim 0.04cm^- 3 if n(H)=0.5cm^- 3. This amount of ionization is considerably
larger than what we expect from primary photoionizations resulting from cosmic
rays, the diffuse X-ray background, and X-ray emitting sources within the
medium, along with the additional ionizations caused by energetic secondary
photoelectrons, Auger electrons, and photons from helium recombinations. We
favor an explanation that bursts of radiation created by previous, nearby
supernova remnants that have faded by now may have elevated the ionization, and
the gas has not yet recombined to a quiescent level. A different alternative is
that the low energy portion of the soft X ray background is poorly shielded by
the H I because it is frothy and has internal pockets of very hot, X-ray
emitting gases.
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO])
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO]):
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Super-Eddington accreting massive black holes as long-lived cosmological standards. (arXiv:1301.4225v1 [astro-ph.CO])
Super-Eddington accreting massive black holes as long-lived cosmological standards. (arXiv:1301.4225v1 [astro-ph.CO]):
Super-Eddington accreting massive black holes (SEAMBHs) reach saturated
luminosities above a certain accretion rate due to photon trapping and
advection in slim accretion disks. We show that these SEAMBHs could provide a
new tool for estimating cosmological distances if they are properly identified
by hard X-ray observations, in particular by the slope of their 2-10 keV
continuum. To verify this idea we obtained black hole mass estimates and X-ray
data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be
the most promising SEAMBH candidates. We demonstrate that the distances derived
by the new method for the objects in the sample get closer to the standard
luminosity distances as the hard X-ray continuum gets steeper. The results
allow us to analyze the requirements for using the method in future samples of
active black holes and to demonstrate that the expected uncertainty, given
large enough samples, can make them into a useful, new cosmological ruler.
Super-Eddington accreting massive black holes (SEAMBHs) reach saturated
luminosities above a certain accretion rate due to photon trapping and
advection in slim accretion disks. We show that these SEAMBHs could provide a
new tool for estimating cosmological distances if they are properly identified
by hard X-ray observations, in particular by the slope of their 2-10 keV
continuum. To verify this idea we obtained black hole mass estimates and X-ray
data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be
the most promising SEAMBH candidates. We demonstrate that the distances derived
by the new method for the objects in the sample get closer to the standard
luminosity distances as the hard X-ray continuum gets steeper. The results
allow us to analyze the requirements for using the method in future samples of
active black holes and to demonstrate that the expected uncertainty, given
large enough samples, can make them into a useful, new cosmological ruler.
Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes. (arXiv:1301.4922v1 [astro-ph.HE])
Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes. (arXiv:1301.4922v1 [astro-ph.HE]):
X-ray irradiation of the accretion disc leads to strong reflection features,
which are then broadened and distorted by relativistic effects. We present a
detailed, general relativistic approach to model this irradiation for different
geometries of the primary X-ray source. These geometries include the standard
point source on the rotational axis as well as more jet-like sources, which are
radially elongated and accelerating. Incorporating this code in the relline
model for relativistic line emission, the line shape for any configuration can
be predicted. We study how different irradiation geometries affect the
determination of the spin of the black hole. Broad emission lines are produced
only for compact irradiating sources situated close to the black hole. This is
the only case where the black hole spin can be unambiguously determined. In all
other cases the line shape is narrower, which could either be explained by a
low spin or an elongated source. We conclude that for all those cases and
independent of the quality of the data, no unique solution for the spin value
exists.
X-ray irradiation of the accretion disc leads to strong reflection features,
which are then broadened and distorted by relativistic effects. We present a
detailed, general relativistic approach to model this irradiation for different
geometries of the primary X-ray source. These geometries include the standard
point source on the rotational axis as well as more jet-like sources, which are
radially elongated and accelerating. Incorporating this code in the relline
model for relativistic line emission, the line shape for any configuration can
be predicted. We study how different irradiation geometries affect the
determination of the spin of the black hole. Broad emission lines are produced
only for compact irradiating sources situated close to the black hole. This is
the only case where the black hole spin can be unambiguously determined. In all
other cases the line shape is narrower, which could either be explained by a
low spin or an elongated source. We conclude that for all those cases and
independent of the quality of the data, no unique solution for the spin value
exists.
A scientific case for future X-ray Astronomy: Galaxy Clusters at high redshifts. (arXiv:1301.5202v1 [astro-ph.CO])
A scientific case for future X-ray Astronomy: Galaxy Clusters at high redshifts. (arXiv:1301.5202v1 [astro-ph.CO]):
Clusters of galaxies at high redshift (z>1) are vitally important to
understand the evolution of the large scale structure of the Universe, the
processes shaping galaxy populations and the cycle of the cosmic baryons, and
to constrain cosmological parameters. After 13 years of operation of the
Chandra and XMM-Newton satellites, the discovery and characterization of
distant X-ray clusters is proceeding at a slow pace, due to the low solid angle
covered so far, and the time-expensive observations needed to physically
characterize their intracluster medium (ICM). At present, we know that at z>1
many massive clusters are fully virialized, their ICM is already enriched with
metals, strong cool cores are already in place, and significant star formation
is ongoing in their most massive galaxies, at least at z>1.4. Clearly, the
assembly of a large and well characterized sample of high-z X-ray clusters is a
major goal for the future. We argue that the only means to achieve this is a
survey-optimized X-ray mission capable of offering large solid angle, high
sensitivity, good spectral coverage, low background and angular resolution as
good as 5 arcsec.
Clusters of galaxies at high redshift (z>1) are vitally important to
understand the evolution of the large scale structure of the Universe, the
processes shaping galaxy populations and the cycle of the cosmic baryons, and
to constrain cosmological parameters. After 13 years of operation of the
Chandra and XMM-Newton satellites, the discovery and characterization of
distant X-ray clusters is proceeding at a slow pace, due to the low solid angle
covered so far, and the time-expensive observations needed to physically
characterize their intracluster medium (ICM). At present, we know that at z>1
many massive clusters are fully virialized, their ICM is already enriched with
metals, strong cool cores are already in place, and significant star formation
is ongoing in their most massive galaxies, at least at z>1.4. Clearly, the
assembly of a large and well characterized sample of high-z X-ray clusters is a
major goal for the future. We argue that the only means to achieve this is a
survey-optimized X-ray mission capable of offering large solid angle, high
sensitivity, good spectral coverage, low background and angular resolution as
good as 5 arcsec.
Structure of neutron stars in R-squared gravity. (arXiv:1301.5189v1 [astro-ph.CO])
Structure of neutron stars in R-squared gravity. (arXiv:1301.5189v1 [astro-ph.CO]):
The effects implied for the structure of compact objects by the modification
of General Relativity produced by the generalization of the Lagrangian density
to the form f(R)=R+\alpha R^2, where R is the Ricci curvature scalar, have been
recently explored. It seems likely that this squared-gravity may allow heavier
Neutron Stars (NSs) than GR. In addition, these objects can be useful to
constrain free parameters of modified-gravity theories. The differences between
alternative gravity theories is enhanced in the strong gravitational regime. In
this regime, because of the complexity of the field equations, perturbative
methods become a good choice to treat the problem. Following previous works in
the field, we performed a numerical integration of the structure equations that
describe NSs in f(R)-gravity, recovering their mass-radius relations, but
focusing on particular features that arise from this approach in the profiles
of the NS interior.
We show that these profiles run in correlation with the second-order
derivative of the analytic approximation to the Equation of State (EoS), which
leads to regions where the enclosed mass decreases with the radius in a
counter-intuitive way. We reproduce all computations with a simple polytropic
EoS to separate zeroth-order modified gravity effects.
The effects implied for the structure of compact objects by the modification
of General Relativity produced by the generalization of the Lagrangian density
to the form f(R)=R+\alpha R^2, where R is the Ricci curvature scalar, have been
recently explored. It seems likely that this squared-gravity may allow heavier
Neutron Stars (NSs) than GR. In addition, these objects can be useful to
constrain free parameters of modified-gravity theories. The differences between
alternative gravity theories is enhanced in the strong gravitational regime. In
this regime, because of the complexity of the field equations, perturbative
methods become a good choice to treat the problem. Following previous works in
the field, we performed a numerical integration of the structure equations that
describe NSs in f(R)-gravity, recovering their mass-radius relations, but
focusing on particular features that arise from this approach in the profiles
of the NS interior.
We show that these profiles run in correlation with the second-order
derivative of the analytic approximation to the Equation of State (EoS), which
leads to regions where the enclosed mass decreases with the radius in a
counter-intuitive way. We reproduce all computations with a simple polytropic
EoS to separate zeroth-order modified gravity effects.
Long Term Variability of O VII Line Intensity toward the Lockman Hole Observed with Suzaku from 2006 to 2011. (arXiv:1301.5174v1 [astro-ph.HE])
Long Term Variability of O VII Line Intensity toward the Lockman Hole Observed with Suzaku from 2006 to 2011. (arXiv:1301.5174v1 [astro-ph.HE]):
Long-term time variabilities of the OVII (0.57 keV) emission in the soft
X-ray diffuse background were studied using six Suzaku annual observations of
blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals
in which the emission was enhanced on time scales of a few tens of ks were
removed, the O VII intensity was found to be constant from 2006 to 2009 within
the 90% statistical errors. The intensity in 2010 and 2011 was higher by 2-3 LU
(photons/s/cm/sr) than the earlier values. The most plausible origin of the
fast variable component is Solar wind charge exchange (SWCX). The intensity
increase is not positively correlated with the proton flux at the L1 point.
Since all the observations were made in the same season of a year, the
variation cannot be explained by parallax of the SWCX induced X-ray emission
from the Heliosphere. We consider that it is related to the geometrical change
of slow and fast solar wind structures associated with the 11 year solar
activity. The observed variation was compared with that expected from the SWCX
induced X-ray emission model.
Long-term time variabilities of the OVII (0.57 keV) emission in the soft
X-ray diffuse background were studied using six Suzaku annual observations of
blank sky towards the Lockman Hole made from 2006 to 2011. After time intervals
in which the emission was enhanced on time scales of a few tens of ks were
removed, the O VII intensity was found to be constant from 2006 to 2009 within
the 90% statistical errors. The intensity in 2010 and 2011 was higher by 2-3 LU
(photons/s/cm/sr) than the earlier values. The most plausible origin of the
fast variable component is Solar wind charge exchange (SWCX). The intensity
increase is not positively correlated with the proton flux at the L1 point.
Since all the observations were made in the same season of a year, the
variation cannot be explained by parallax of the SWCX induced X-ray emission
from the Heliosphere. We consider that it is related to the geometrical change
of slow and fast solar wind structures associated with the 11 year solar
activity. The observed variation was compared with that expected from the SWCX
induced X-ray emission model.
A detailed X-ray investigation of {\zeta} Puppis III. A spectral analysis of the whole RGS spectrum. (arXiv:1301.5090v1 [astro-ph.SR])
A detailed X-ray investigation of {\zeta} Puppis III. A spectral analysis of the whole RGS spectrum. (arXiv:1301.5090v1 [astro-ph.SR]):
Context. Zeta Pup is the X-ray brightest O-type star of the sky. This object
was regularly observed with the RGS instrument aboard XMM-Newton for
calibration purposes, leading to an unprecedented set of high-quality spectra.
Aims. We have previously reduced and extracted this data set and combined it
into the most detailed high-resolution X-ray spectrum of any early-type star so
far. Here we present the analysis of this spectrum accounting for the presence
of structures in the stellar wind. Methods. For this purpose, we use our new
modeling tool that allows fitting the entire spectrum with a multi-temperature
plasma. We illustrate the impact of a proper treatment of the radial dependence
of the X-ray opacity of the cool wind on the best-fit radial distribution of
the temperature of the X-ray plasma. Results. The best fit of the RGS spectrum
of Zeta Pup is obtained assuming no porosity. Four plasma components at
temperatures between 0.10 and 0.69 keV are needed to adequately represent the
observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4
R*, the softer emission starts already at 1.5 R* and extends to the outer
regions of the wind. Conclusions. The inferred radial distribution of the
plasma temperatures agrees rather well with theoretical expectations. The mass-
loss rate and CNO abundances corresponding to our best-fit model also agree
quite well with the results of recent studies of Zeta Pup in the UV and optical
domain.
Context. Zeta Pup is the X-ray brightest O-type star of the sky. This object
was regularly observed with the RGS instrument aboard XMM-Newton for
calibration purposes, leading to an unprecedented set of high-quality spectra.
Aims. We have previously reduced and extracted this data set and combined it
into the most detailed high-resolution X-ray spectrum of any early-type star so
far. Here we present the analysis of this spectrum accounting for the presence
of structures in the stellar wind. Methods. For this purpose, we use our new
modeling tool that allows fitting the entire spectrum with a multi-temperature
plasma. We illustrate the impact of a proper treatment of the radial dependence
of the X-ray opacity of the cool wind on the best-fit radial distribution of
the temperature of the X-ray plasma. Results. The best fit of the RGS spectrum
of Zeta Pup is obtained assuming no porosity. Four plasma components at
temperatures between 0.10 and 0.69 keV are needed to adequately represent the
observed spectrum. Whilst the hardest emission is concentrated between ~3 and 4
R*, the softer emission starts already at 1.5 R* and extends to the outer
regions of the wind. Conclusions. The inferred radial distribution of the
plasma temperatures agrees rather well with theoretical expectations. The mass-
loss rate and CNO abundances corresponding to our best-fit model also agree
quite well with the results of recent studies of Zeta Pup in the UV and optical
domain.
The Structure of the X-ray and Optical Emitting Regions of the Lensed Quasar Q 2237+0305. (arXiv:1301.5009v1 [astro-ph.CO])
The Structure of the X-ray and Optical Emitting Regions of the Lensed Quasar Q 2237+0305. (arXiv:1301.5009v1 [astro-ph.CO]):
We use gravitational microlensing to determine the size of the X-ray and
optical emission regions of the quadruple lens system Q 2237+0305. The optical
half-light radius, log(R_{1/2,V}/cm)=16.41\pm0.18 (at lambda_{rest}=2018 \AA),
is significantly larger than the observed soft,
log(R_{1/2,soft}/cm)=15.76^{+0.41}_{-0.34} (1.1-3.5 keV in the rest frame), and
hard, log(R_{1/2,hard}/cm)=15.46^{+0.34}_{-0.29} (3.5-21.5 keV in the rest
frame), band X-ray emission. There is a weak evidence that the hard component
is more compact than the soft, with log(R_{1/2,soft}/R_{1/2,hard}) \sim
0.30^{+0.53}_{-0.45}. This wavelength-dependent structure agrees with recent
results found in other lens systems using microlensing techniques, and favors
geometries in which the corona is concentrated near the inner edge of the
accretion disk. While the available measurements are limited, the size of the
X-ray emission region appears to be roughly proportional to the mass of the
central black hole.
We use gravitational microlensing to determine the size of the X-ray and
optical emission regions of the quadruple lens system Q 2237+0305. The optical
half-light radius, log(R_{1/2,V}/cm)=16.41\pm0.18 (at lambda_{rest}=2018 \AA),
is significantly larger than the observed soft,
log(R_{1/2,soft}/cm)=15.76^{+0.41}_{-0.34} (1.1-3.5 keV in the rest frame), and
hard, log(R_{1/2,hard}/cm)=15.46^{+0.34}_{-0.29} (3.5-21.5 keV in the rest
frame), band X-ray emission. There is a weak evidence that the hard component
is more compact than the soft, with log(R_{1/2,soft}/R_{1/2,hard}) \sim
0.30^{+0.53}_{-0.45}. This wavelength-dependent structure agrees with recent
results found in other lens systems using microlensing techniques, and favors
geometries in which the corona is concentrated near the inner edge of the
accretion disk. While the available measurements are limited, the size of the
X-ray emission region appears to be roughly proportional to the mass of the
central black hole.
Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO])
Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO]):
In this study we present three-dimensional radiative cooling hydrodynamical
simulations of galactic winds generated particularly in M82-like starburst
galaxies. We have considered intermittent winds induced by SNe explosions
within super star clusters randomly distributed in the central region of the
galaxy and were able to reproduce the observed M82 wind conditions with its
complex morphological outflow structure. We have found that the environmental
conditions in the disk in nearly recent past are crucial to determine whether
the wind will develop a large scale rich filamentary structure, as in M82 wind,
or not. Also, the numerical evolution of the SN ejecta have allowed us to
obtain the abundance distribution over the first 3 kpc extension of the wind
and we have found that the SNe explosions change significantly the metallicity
only of the hot, low-density wind component. Moreover, we have found that the
SN-driven wind transports to outside the disk large amounts of energy, momentum
and gas, but the more massive high-density component reaches only intermediate
altitudes smaller than 1.5 kpc. Therefore, no significant amounts of gas mass
are lost to the IGM and the mass evolution of the galaxy is not much affected
by the starburst events occurring in the nuclear region.
In this study we present three-dimensional radiative cooling hydrodynamical
simulations of galactic winds generated particularly in M82-like starburst
galaxies. We have considered intermittent winds induced by SNe explosions
within super star clusters randomly distributed in the central region of the
galaxy and were able to reproduce the observed M82 wind conditions with its
complex morphological outflow structure. We have found that the environmental
conditions in the disk in nearly recent past are crucial to determine whether
the wind will develop a large scale rich filamentary structure, as in M82 wind,
or not. Also, the numerical evolution of the SN ejecta have allowed us to
obtain the abundance distribution over the first 3 kpc extension of the wind
and we have found that the SNe explosions change significantly the metallicity
only of the hot, low-density wind component. Moreover, we have found that the
SN-driven wind transports to outside the disk large amounts of energy, momentum
and gas, but the more massive high-density component reaches only intermediate
altitudes smaller than 1.5 kpc. Therefore, no significant amounts of gas mass
are lost to the IGM and the mass evolution of the galaxy is not much affected
by the starburst events occurring in the nuclear region.
Sunday, January 20, 2013
Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies. (arXiv:1301.3200v1 [astro-ph.CO])
Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies. (arXiv:1301.3200v1 [astro-ph.CO]):
The amount of metals in the Intracluster Medium (ICM) in rich galaxy clusters
exceeds that expected based on the observed stellar population by a large
factor. We quantify this discrepancy -- which we term the "cluster elemental
abundance paradox" -- and investigate the required properties of the
ICM-enriching population. The necessary enhancement in metal enrichment may, in
principle, originate in the observed stellar population if a larger fraction of
stars in the supernova-progenitor mass range form from an initial mass function
(IMF) that is either bottom-light or top-heavy, with the latter in some
conflict with observed ICM abundance ratios. Other alternatives that imply more
modest revisions to the IMF, mass return and remnant fractions, and primordial
fraction, posit an increase in the fraction of 3-8 solar mass stars that
explode as SNIa or assume that there are more stars than conventionally thought
-- although the latter implies a high star formation efficiency. We discuss the
feasibility of these various solutions and the implications for the diversity
of star formation, the process of elliptical galaxy formation, and the nature
of this "hidden" source of ICM metal enrichment in light of recent evidence of
an elliptical galaxy IMF that, because it is skewed to low masses, deepens the
paradox.
The amount of metals in the Intracluster Medium (ICM) in rich galaxy clusters
exceeds that expected based on the observed stellar population by a large
factor. We quantify this discrepancy -- which we term the "cluster elemental
abundance paradox" -- and investigate the required properties of the
ICM-enriching population. The necessary enhancement in metal enrichment may, in
principle, originate in the observed stellar population if a larger fraction of
stars in the supernova-progenitor mass range form from an initial mass function
(IMF) that is either bottom-light or top-heavy, with the latter in some
conflict with observed ICM abundance ratios. Other alternatives that imply more
modest revisions to the IMF, mass return and remnant fractions, and primordial
fraction, posit an increase in the fraction of 3-8 solar mass stars that
explode as SNIa or assume that there are more stars than conventionally thought
-- although the latter implies a high star formation efficiency. We discuss the
feasibility of these various solutions and the implications for the diversity
of star formation, the process of elliptical galaxy formation, and the nature
of this "hidden" source of ICM metal enrichment in light of recent evidence of
an elliptical galaxy IMF that, because it is skewed to low masses, deepens the
paradox.
Chaotic cold accretion onto black holes. (arXiv:1301.3130v1 [astro-ph.CO])
Chaotic cold accretion onto black holes. (arXiv:1301.3130v1 [astro-ph.CO]):
Using 3D AMR simulations, linking the 50 kpc to the sub-pc scales over the
course of 40 Myr, we systematically relax the classic Bondi assumptions in a
typical galaxy hosting a SMBH. In the realistic scenario, where the hot gas is
cooling, while heated and stirred on large scales, the accretion rate is
boosted up to two orders of magnitude compared with the Bondi prediction. The
cause is the nonlinear growth of thermal instabilities, leading to the
condensation of cold clouds and filaments when t_cool/t_ff < 10. Subsonic
turbulence of just over 100 km/s (M > 0.2) induces the formation of thermal
instabilities, even in the absence of heating, while in the transonic regime
turbulent dissipation inhibits their growth (t_turb/t_cool < 1). When heating
restores global thermodynamic balance, the formation of the multiphase medium
is violent, and the mode of accretion is fully cold and chaotic. The recurrent
collisions, shearing and tidal motions between clouds, filaments and the
central torus cause a significant reduction of angular momentum, boosting
accretion. On sub-pc scales the clouds are channelled to the very centre via a
funnel. A good approximation to the accretion rate is the cooling rate, which
can be used as subgrid model, physically reproducing the boost factor of 100
required by cosmological simulations, while accounting for fluctuations.
Chaotic cold accretion may be common in many systems, such as hot galactic
halos, groups, and clusters, generating high-velocity clouds and strong
variations of the AGN luminosity, jet orientation, and spin. In this mode, the
black hole can quickly react to the state of the entire host galaxy, leading to
efficient self-regulated feedback and the symbiotic Magorrian relation. During
phases of overheating, the hot mode becomes the single channel of accretion
(with a different cuspy temperature profile), though strongly suppressed by
turbulence.
Using 3D AMR simulations, linking the 50 kpc to the sub-pc scales over the
course of 40 Myr, we systematically relax the classic Bondi assumptions in a
typical galaxy hosting a SMBH. In the realistic scenario, where the hot gas is
cooling, while heated and stirred on large scales, the accretion rate is
boosted up to two orders of magnitude compared with the Bondi prediction. The
cause is the nonlinear growth of thermal instabilities, leading to the
condensation of cold clouds and filaments when t_cool/t_ff < 10. Subsonic
turbulence of just over 100 km/s (M > 0.2) induces the formation of thermal
instabilities, even in the absence of heating, while in the transonic regime
turbulent dissipation inhibits their growth (t_turb/t_cool < 1). When heating
restores global thermodynamic balance, the formation of the multiphase medium
is violent, and the mode of accretion is fully cold and chaotic. The recurrent
collisions, shearing and tidal motions between clouds, filaments and the
central torus cause a significant reduction of angular momentum, boosting
accretion. On sub-pc scales the clouds are channelled to the very centre via a
funnel. A good approximation to the accretion rate is the cooling rate, which
can be used as subgrid model, physically reproducing the boost factor of 100
required by cosmological simulations, while accounting for fluctuations.
Chaotic cold accretion may be common in many systems, such as hot galactic
halos, groups, and clusters, generating high-velocity clouds and strong
variations of the AGN luminosity, jet orientation, and spin. In this mode, the
black hole can quickly react to the state of the entire host galaxy, leading to
efficient self-regulated feedback and the symbiotic Magorrian relation. During
phases of overheating, the hot mode becomes the single channel of accretion
(with a different cuspy temperature profile), though strongly suppressed by
turbulence.
Mass/Radius Constraints on the Quiescent Neutron Star in M13 Using Hydrogen and Helium Atmospheres. (arXiv:1301.3768v1 [astro-ph.HE])
Mass/Radius Constraints on the Quiescent Neutron Star in M13 Using Hydrogen and Helium Atmospheres. (arXiv:1301.3768v1 [astro-ph.HE]):
The mass and radius of the neutron star (NS) in low-mass X-ray binaries can
be obtained by fitting the X-ray spectrum of the NS in quiescence, and the mass
and radius constrains the properties of dense matter in NS cores. A critical
ingredient for spectral fits is the composition of the NS atmosphere: hydrogen
atmospheres are assumed in most prior work, but helium atmospheres are possible
if the donor star is a helium white dwarf. Here we perform spectral fits to
XMM, Chandra, and ROSAT data of a quiescent NS in the globular cluster M13.
This NS has the smallest inferred radius from previous spectral fitting.
Assuming an atmosphere composed of hydrogen, we find a significantly larger
radius, more consistent with those from other quiescent NSs. With a helium
atmosphere (an equally acceptable fit), we find even larger values for the
radius.
The mass and radius of the neutron star (NS) in low-mass X-ray binaries can
be obtained by fitting the X-ray spectrum of the NS in quiescence, and the mass
and radius constrains the properties of dense matter in NS cores. A critical
ingredient for spectral fits is the composition of the NS atmosphere: hydrogen
atmospheres are assumed in most prior work, but helium atmospheres are possible
if the donor star is a helium white dwarf. Here we perform spectral fits to
XMM, Chandra, and ROSAT data of a quiescent NS in the globular cluster M13.
This NS has the smallest inferred radius from previous spectral fitting.
Assuming an atmosphere composed of hydrogen, we find a significantly larger
radius, more consistent with those from other quiescent NSs. With a helium
atmosphere (an equally acceptable fit), we find even larger values for the
radius.
The Radio-X-ray Connection in Young Stellar Objects in the Orion Nebula Cluster. (arXiv:1301.3739v1 [astro-ph.SR])
The Radio-X-ray Connection in Young Stellar Objects in the Orion Nebula Cluster. (arXiv:1301.3739v1 [astro-ph.SR]):
(Abridged) Context: Both X-ray and radio observations offer insight into the
high-energy processes of young stellar objects (YSOs). The observed thermal
X-ray emission can be accompanied by both thermal and nonthermal radio
emission. Due to variability, simultaneous X-ray and radio observations are a
priori required, but results have been inconclusive. Aims: We use archival
X-ray and radio observations of the Orion Nebula Cluster (ONC) to significantly
enlarge the sample size of known YSOs with both X-ray and radio detections.
Methods: We study the ONC using multi-epoch non-simultaneous archival Chandra
X-ray and NRAO Very Large Array (VLA) single-band radio data. The multiple
epochs allow us to reduce the impact of variability by obtaining approximated
quiescent fluxes. Results: We find that only a small fraction of the X-ray
sources (7%) have radio counterparts, even if 60% of the radio sources have
X-ray counterparts. The radio flux density is typically too low to distinguish
thermal and nonthermal radio sources. Only a small fraction of the YSOs with
detections in both bands are compatible with the empirical "Guedel-Benz" (GB)
relation. Most of the sources not compatible with the GB relation are proplyds,
and thus likely thermal sources, but only a fraction of the proplyds is
detected in both bands, such that the role of these sources is inconclusive.
Conclusions: While the radio sources appear to be globally unrelated to the
X-ray sources, the X-ray dataset clearly is much more sensitive than the radio
data. We find tentative evidence that known non-thermal radio sources and
saturated X-ray sources are indeed close to the empirical relation, even if
skewed to higher radio luminosities, as they are expected to be. Most of the
sources that are clearly incompatible with the empirical relation are proplyds
which could instead plausibly be thermal radio sources.
(Abridged) Context: Both X-ray and radio observations offer insight into the
high-energy processes of young stellar objects (YSOs). The observed thermal
X-ray emission can be accompanied by both thermal and nonthermal radio
emission. Due to variability, simultaneous X-ray and radio observations are a
priori required, but results have been inconclusive. Aims: We use archival
X-ray and radio observations of the Orion Nebula Cluster (ONC) to significantly
enlarge the sample size of known YSOs with both X-ray and radio detections.
Methods: We study the ONC using multi-epoch non-simultaneous archival Chandra
X-ray and NRAO Very Large Array (VLA) single-band radio data. The multiple
epochs allow us to reduce the impact of variability by obtaining approximated
quiescent fluxes. Results: We find that only a small fraction of the X-ray
sources (7%) have radio counterparts, even if 60% of the radio sources have
X-ray counterparts. The radio flux density is typically too low to distinguish
thermal and nonthermal radio sources. Only a small fraction of the YSOs with
detections in both bands are compatible with the empirical "Guedel-Benz" (GB)
relation. Most of the sources not compatible with the GB relation are proplyds,
and thus likely thermal sources, but only a fraction of the proplyds is
detected in both bands, such that the role of these sources is inconclusive.
Conclusions: While the radio sources appear to be globally unrelated to the
X-ray sources, the X-ray dataset clearly is much more sensitive than the radio
data. We find tentative evidence that known non-thermal radio sources and
saturated X-ray sources are indeed close to the empirical relation, even if
skewed to higher radio luminosities, as they are expected to be. Most of the
sources that are clearly incompatible with the empirical relation are proplyds
which could instead plausibly be thermal radio sources.
The largest mid-infrared atlas of active galactic nuclei at sub-arcsecond spatial scales. (arXiv:1301.3680v1 [astro-ph.CO])
The largest mid-infrared atlas of active galactic nuclei at sub-arcsecond spatial scales. (arXiv:1301.3680v1 [astro-ph.CO]):
We present the largest mid-infrared atlas of active galactic nuclei at
sub-arcsecond spatial scales containing 249 objects. It comprises all
ground-based HR MIR observations performed to date. This catalog includes a
large number of new observations. The photometry in multiple filters allows for
characterizing the properties of the dust emission for most objects. Because of
its size and characteristics, this sample is very well-suited for AGN
unification studies. In particular, we discuss the enlarged MIR--X-ray
correlation which extends over six orders of magnitude in luminosity and
potentially probes different physical mechanisms. Finally, tests for intrinsic
differences between the AGN types are presented and we discuss dependencies of
MIR--X-ray properties with respect to fundamental AGN parameters such as
accretion rate and the column density and covering factor of obscuring
material.
We present the largest mid-infrared atlas of active galactic nuclei at
sub-arcsecond spatial scales containing 249 objects. It comprises all
ground-based HR MIR observations performed to date. This catalog includes a
large number of new observations. The photometry in multiple filters allows for
characterizing the properties of the dust emission for most objects. Because of
its size and characteristics, this sample is very well-suited for AGN
unification studies. In particular, we discuss the enlarged MIR--X-ray
correlation which extends over six orders of magnitude in luminosity and
potentially probes different physical mechanisms. Finally, tests for intrinsic
differences between the AGN types are presented and we discuss dependencies of
MIR--X-ray properties with respect to fundamental AGN parameters such as
accretion rate and the column density and covering factor of obscuring
material.
Distant galaxy clusters in a deep XMM-Newton field within the CFTHLS D4. (arXiv:1301.3506v1 [astro-ph.CO])
Distant galaxy clusters in a deep XMM-Newton field within the CFTHLS D4. (arXiv:1301.3506v1 [astro-ph.CO]):
The XMM-Newton Distant Cluster Project (XDCP) aims at the identification of a
well defined sample of X-ray selected clusters of galaxies at redshifts z>0.8.
We present a catalogue of the extended sources in one the deepest ~250 ksec
XMM-Newton fields targeting LBQS 2215-175 covering the CFHTLS deep field four.
The cluster identification is based, among others, on deep imaging with the ESO
VLT and from the CFHT legacy survey. The confirmation of cluster candidates is
done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the
CFHTLS D4 are utilized to confirm the effectiveness of the X-ray cluster
selection method. The survey sensitivity is computed with extensive
simulations. At a flux limit of S(0.5-2.0 keV) ~ 2.5e-15 erg/s we achieve a
completeness level higher than 50% in an area of ~0.13 square degrees. We
detect six galaxy clusters above this limit with optical counterparts, of which
5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy
clusters are at z>1.0, another two at z=0.41 and one at z=0.34. For the most
distant X-ray selected cluster in this field at z=1.45 we find additional
(active) member galaxies from both X-ray and spectroscopic data. Additionally,
we find evidence of large scale structures at moderate redshifts of z=0.41 and
z=0.34. The quest for distant clusters in archival XMM-Newton data has led to
the detection of six clusters in a single field, making XMM-Newton an
outstanding tool for cluster surveys. Three of these clusters are at z>1, which
emphasises the valuable contribution of small, yet deep surveys to cosmology.
Beta-models are appropriate descriptions for the cluster surface brightness to
perform cluster detection simulations in order to compute the X-ray selection
function. The constructed logN-logS tends to favour a scenario where no
evolution in the cluster X-ray luminosity function (XLF) takes place.
The XMM-Newton Distant Cluster Project (XDCP) aims at the identification of a
well defined sample of X-ray selected clusters of galaxies at redshifts z>0.8.
We present a catalogue of the extended sources in one the deepest ~250 ksec
XMM-Newton fields targeting LBQS 2215-175 covering the CFHTLS deep field four.
The cluster identification is based, among others, on deep imaging with the ESO
VLT and from the CFHT legacy survey. The confirmation of cluster candidates is
done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the
CFHTLS D4 are utilized to confirm the effectiveness of the X-ray cluster
selection method. The survey sensitivity is computed with extensive
simulations. At a flux limit of S(0.5-2.0 keV) ~ 2.5e-15 erg/s we achieve a
completeness level higher than 50% in an area of ~0.13 square degrees. We
detect six galaxy clusters above this limit with optical counterparts, of which
5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy
clusters are at z>1.0, another two at z=0.41 and one at z=0.34. For the most
distant X-ray selected cluster in this field at z=1.45 we find additional
(active) member galaxies from both X-ray and spectroscopic data. Additionally,
we find evidence of large scale structures at moderate redshifts of z=0.41 and
z=0.34. The quest for distant clusters in archival XMM-Newton data has led to
the detection of six clusters in a single field, making XMM-Newton an
outstanding tool for cluster surveys. Three of these clusters are at z>1, which
emphasises the valuable contribution of small, yet deep surveys to cosmology.
Beta-models are appropriate descriptions for the cluster surface brightness to
perform cluster detection simulations in order to compute the X-ray selection
function. The constructed logN-logS tends to favour a scenario where no
evolution in the cluster X-ray luminosity function (XLF) takes place.
Discovery of X-ray emission from young suns in the Small Magellanic Cloud. (arXiv:1301.3500v1 [astro-ph.SR])
Discovery of X-ray emission from young suns in the Small Magellanic Cloud. (arXiv:1301.3500v1 [astro-ph.SR]):
We report the discovery of extended X-ray emission within the young star
cluster NGC 602 in the Wing of the Small Magellanic Cloud (SMC) based on
observations obtained with the Chandra X-ray Observatory. X-ray emission is
detected from the cluster core area with the highest stellar density and from a
dusty ridge surrounding the HII region. We use a census of massive stars in the
cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to
provide a significant contribution to the X-ray emission detected from the
central area of the cluster. We therefore suggest that X-ray emission at the
cluster core originates from an ensemble of low- and solar-mass
pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be
detected individually. We attribute the X-ray emission from the dusty ridge to
the embedded tight cluster of the new-born stars known in this area from
infrared studies. Assuming that the levels of X-ray activity in young stars in
the low-metallicity environment of NGC 602a are comparable to their Galactic
counterparts, then the detected spatial distribution, spectral properties, and
level of X-ray emission are largely consistent with those expected from low-
and solar-mass PMS stars and young stellar objects (YSOs). This is the first
discovery of X-ray emission attributable to PMS stars and YSOs in the SMC,
which suggests that the accretion and dynamo processes in young, low-mass
objects in the SMC resemble those in the Galaxy.
We report the discovery of extended X-ray emission within the young star
cluster NGC 602 in the Wing of the Small Magellanic Cloud (SMC) based on
observations obtained with the Chandra X-ray Observatory. X-ray emission is
detected from the cluster core area with the highest stellar density and from a
dusty ridge surrounding the HII region. We use a census of massive stars in the
cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to
provide a significant contribution to the X-ray emission detected from the
central area of the cluster. We therefore suggest that X-ray emission at the
cluster core originates from an ensemble of low- and solar-mass
pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be
detected individually. We attribute the X-ray emission from the dusty ridge to
the embedded tight cluster of the new-born stars known in this area from
infrared studies. Assuming that the levels of X-ray activity in young stars in
the low-metallicity environment of NGC 602a are comparable to their Galactic
counterparts, then the detected spatial distribution, spectral properties, and
level of X-ray emission are largely consistent with those expected from low-
and solar-mass PMS stars and young stellar objects (YSOs). This is the first
discovery of X-ray emission attributable to PMS stars and YSOs in the SMC,
which suggests that the accretion and dynamo processes in young, low-mass
objects in the SMC resemble those in the Galaxy.
AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes. (arXiv:1301.3499v1 [astro-ph.CO])
AGN Jet Kinetic Power and the Energy Budget of Radio Galaxy Lobes. (arXiv:1301.3499v1 [astro-ph.CO]):
Recent results based on the analysis of radio galaxies and their hot X-ray
emitting atmospheres suggest that non-radiating particles dominate the energy
budget in the lobes of FRI radio galaxies, in some cases by a factor of more
than 1000, while radiating particles dominate the energy budget in FRII radio
galaxy lobes. This implies a significant difference in the radiative efficiency
of the two morphological classes. To test this hypothesis, we have measured the
kinetic energy flux for a sample of 3C FRII radio sources using a new method
based on the observed parameters of the jet terminal hotspots, and compared the
resulting Q(jet) - L(radio) relation to that obtained for FRI radio galaxies
based on X-ray cavity measurements. Contrary to expectations, we find
approximate agreement between the Q(jet) - L(radio) relations determined
separately for FRI and FRII radio galaxies. This result is ostensibly difficult
to reconcile with the emerging scenario in which the lobes of FRI and FRII
radio galaxies have vastly different energy budgets. However, a combination of
lower density environment, spectral ageing and strong shocks driven by powerful
FRII radio galaxies may reduce the radiative efficiency of these objects
relative to FRIs and couteract, to some extent, the higher radiative efficiency
expected to arise due to the lower fraction of energy in non-radiating
particles. An unexpected corollary is that extrapolating the Q(jet) - L(radio)
relation determined for low power FRI radio galaxies provides a reasonable
approximation for high power sources, despite their apparently different lobe
compositions.
Recent results based on the analysis of radio galaxies and their hot X-ray
emitting atmospheres suggest that non-radiating particles dominate the energy
budget in the lobes of FRI radio galaxies, in some cases by a factor of more
than 1000, while radiating particles dominate the energy budget in FRII radio
galaxy lobes. This implies a significant difference in the radiative efficiency
of the two morphological classes. To test this hypothesis, we have measured the
kinetic energy flux for a sample of 3C FRII radio sources using a new method
based on the observed parameters of the jet terminal hotspots, and compared the
resulting Q(jet) - L(radio) relation to that obtained for FRI radio galaxies
based on X-ray cavity measurements. Contrary to expectations, we find
approximate agreement between the Q(jet) - L(radio) relations determined
separately for FRI and FRII radio galaxies. This result is ostensibly difficult
to reconcile with the emerging scenario in which the lobes of FRI and FRII
radio galaxies have vastly different energy budgets. However, a combination of
lower density environment, spectral ageing and strong shocks driven by powerful
FRII radio galaxies may reduce the radiative efficiency of these objects
relative to FRIs and couteract, to some extent, the higher radiative efficiency
expected to arise due to the lower fraction of energy in non-radiating
particles. An unexpected corollary is that extrapolating the Q(jet) - L(radio)
relation determined for low power FRI radio galaxies provides a reasonable
approximation for high power sources, despite their apparently different lobe
compositions.
Spatially resolved star formation image and the ULX population in NGC2207/IC2163. (arXiv:1301.4084v1 [astro-ph.HE])
Spatially resolved star formation image and the ULX population in NGC2207/IC2163. (arXiv:1301.4084v1 [astro-ph.HE]):
The colliding galaxy pair NGC 2207/IC 2163, at a distance of ~39 Mpc, was
observed with Chandra, and an analysis reveals 22 well resolved, luminous X-ray
sources. Most of these are ultraluminous X-ray sources (ULXs) with Lx>1e+39
erg/s. The number of ULXs is comparable with the largest numbers of ULXs per
unit mass in any galaxy yet reported. In this paper we report on these sources,
and quantify how their locations correlate with the local star formation rates
seen in spatially-resolved star formation rate density images that we have
constructed using combinations of Galex FUV and Spitzer 24{\mu}m images. We
show that the numbers of ULXs are strongly correlated with the local star
formation rate densities surrounding the sources, but that the luminosities of
these sources are not strongly correlated with star formation rate density.
The colliding galaxy pair NGC 2207/IC 2163, at a distance of ~39 Mpc, was
observed with Chandra, and an analysis reveals 22 well resolved, luminous X-ray
sources. Most of these are ultraluminous X-ray sources (ULXs) with Lx>1e+39
erg/s. The number of ULXs is comparable with the largest numbers of ULXs per
unit mass in any galaxy yet reported. In this paper we report on these sources,
and quantify how their locations correlate with the local star formation rates
seen in spatially-resolved star formation rate density images that we have
constructed using combinations of Galex FUV and Spitzer 24{\mu}m images. We
show that the numbers of ULXs are strongly correlated with the local star
formation rate densities surrounding the sources, but that the luminosities of
these sources are not strongly correlated with star formation rate density.
Constraints on the quark matter equation of state from astrophysical observations. (arXiv:1301.4060v1 [nucl-th])
Constraints on the quark matter equation of state from astrophysical observations. (arXiv:1301.4060v1 [nucl-th]):
We calculate the structure of neutron star interiors comprising both the
hadronic and the quark phases. For the hadronic sector we employ a microscopic
equation of state involving nucleons and hyperons derived within the
Brueckner-Hartree-Fock many-body theory with realistic two-body and three-body
forces. For the description of quark matter, we use several different models,
e.g. the MIT bag, the Nambu--Jona-Lasinio (NJL), the Color Dielectric (CDM),
the Field Correlator method (FCM), and one based on the Dyson-Schwinger model
(DSM). We find that a two solar mass hybrid star is possible only if the
nucleonic EOS is stiff enough.
We calculate the structure of neutron star interiors comprising both the
hadronic and the quark phases. For the hadronic sector we employ a microscopic
equation of state involving nucleons and hyperons derived within the
Brueckner-Hartree-Fock many-body theory with realistic two-body and three-body
forces. For the description of quark matter, we use several different models,
e.g. the MIT bag, the Nambu--Jona-Lasinio (NJL), the Color Dielectric (CDM),
the Field Correlator method (FCM), and one based on the Dyson-Schwinger model
(DSM). We find that a two solar mass hybrid star is possible only if the
nucleonic EOS is stiff enough.
Far-Infrared and submillimeter properties of SDSS galaxies in the Herschel ATLAS science demonstration phase field. (arXiv:1301.4001v1 [astro-ph.CO])
Far-Infrared and submillimeter properties of SDSS galaxies in the Herschel ATLAS science demonstration phase field. (arXiv:1301.4001v1 [astro-ph.CO]):
Using the Herschel ATLAS science demonstration phase data crossidentified
with SDSS DR7 spectra, we select 297 galaxies with F250{\mu}m > 5{\sigma}. The
sample galaxies are classified into five morphological types, and more than 40%
of the galaxies are peculiar/compact galaxies. The peculiar galaxies show
higher far-infrared/submillimeter luminosity-to-mass ratios than the other
types. We perform and analyze the correlations of far-infrared/submillimeter
and H{\alpha} luminosities for different morphological types and different
spectral types. The Spearman rank coefficient decreases and the scatter
increases with the wavelength increasing from 100 {\mu}m to 500 {\mu}m. We
conclude that a single Herschel SPIRE band is not good for tracing star
formation activities in galaxies. AGNs contribute less to the
far-infrared/submillimeter luminosities and do not show a difference from
star-forming galaxies. However, the earlier type galaxies present significant
deviations from the best fit of star-forming galaxies.
Using the Herschel ATLAS science demonstration phase data crossidentified
with SDSS DR7 spectra, we select 297 galaxies with F250{\mu}m > 5{\sigma}. The
sample galaxies are classified into five morphological types, and more than 40%
of the galaxies are peculiar/compact galaxies. The peculiar galaxies show
higher far-infrared/submillimeter luminosity-to-mass ratios than the other
types. We perform and analyze the correlations of far-infrared/submillimeter
and H{\alpha} luminosities for different morphological types and different
spectral types. The Spearman rank coefficient decreases and the scatter
increases with the wavelength increasing from 100 {\mu}m to 500 {\mu}m. We
conclude that a single Herschel SPIRE band is not good for tracing star
formation activities in galaxies. AGNs contribute less to the
far-infrared/submillimeter luminosities and do not show a difference from
star-forming galaxies. However, the earlier type galaxies present significant
deviations from the best fit of star-forming galaxies.
X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from Gamma-ray Bursts. (arXiv:1301.3975v1 [astro-ph.HE])
X-ray plateaus followed by sharp drops in GRBs 060413, 060522, 060607A and 080330: Further evidences for central engine afterglow from Gamma-ray Bursts. (arXiv:1301.3975v1 [astro-ph.HE]):
The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are
characterized by plateaus that are followed by very sharp drops. An X-ray
plateau is interpretable within the framework of the external forward shock
model but the sharp drop is not. In this work we interpret these peculiar X-ray
afterglow data as the central engine afterglows from some magnetized central
engines, plausibly magnetars. In this model, the X-ray afterglows are powered
by the internal magnetic energy dissipation and the sudden drop is caused by
the collapse of the magnetar. Accordingly, the X-ray plateau photons should
have a high linear polarization, which can be tested by the future X-ray
polarimetry.
The X-ray afterglows of GRBs 060413, 060522, 060607A and 080330 are
characterized by plateaus that are followed by very sharp drops. An X-ray
plateau is interpretable within the framework of the external forward shock
model but the sharp drop is not. In this work we interpret these peculiar X-ray
afterglow data as the central engine afterglows from some magnetized central
engines, plausibly magnetars. In this model, the X-ray afterglows are powered
by the internal magnetic energy dissipation and the sudden drop is caused by
the collapse of the magnetar. Accordingly, the X-ray plateau photons should
have a high linear polarization, which can be tested by the future X-ray
polarimetry.
The brightest ULIRG:watching the birth of a quasar. (arXiv:1301.3953v1 [astro-ph.CO])
The brightest ULIRG:watching the birth of a quasar. (arXiv:1301.3953v1 [astro-ph.CO]):
The extreme ULIRG F00183-7111 has recently been found to have a radio-loud
AGN with jets in its centre, representing an extreme example of the class of
radio-loud AGNs buried within dusty star-forming galaxies. This source appears
to be a rare example of a ULIRG glimpsed in the (presumably) brief period as it
changes from "quasar mode" to "radio mode" activity. Such transition stages
probably account for many of the high-redshift radio-galaxies and extreme
high-redshift ULIRGs, and so this object at the relatively low redshift of
0.328 offers a rare opportunity to study this class of objects in detail. We
have also detected the CO signal from this galaxy with the ATCA, and here
describe the implications of this detection for future ULIRG studies.
The extreme ULIRG F00183-7111 has recently been found to have a radio-loud
AGN with jets in its centre, representing an extreme example of the class of
radio-loud AGNs buried within dusty star-forming galaxies. This source appears
to be a rare example of a ULIRG glimpsed in the (presumably) brief period as it
changes from "quasar mode" to "radio mode" activity. Such transition stages
probably account for many of the high-redshift radio-galaxies and extreme
high-redshift ULIRGs, and so this object at the relatively low redshift of
0.328 offers a rare opportunity to study this class of objects in detail. We
have also detected the CO signal from this galaxy with the ATCA, and here
describe the implications of this detection for future ULIRG studies.
Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters. (arXiv:1301.3922v1 [astro-ph.CO])
Concurrent Supermassive Black Hole and Galaxy Growth: Linking Environment and Nuclear Activity in z = 2.23 H-alpha Emitters. (arXiv:1301.3922v1 [astro-ph.CO]):
We present results from a ~100 ks Chandra observation of the 2QZ Cluster
1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally
identified as an overdensity of four optically-selected QSOs at z = 2.23 within
a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the
structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting
galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra
observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully
accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of
~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured
AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS),
we find suggestive evidence that the AGN fraction increases with local HAE
galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment
(a factor of ~2 times over the field), and after excluding optically-selected
QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than
C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra
data and Herschel SPIRE observations at 250 um, we respectively estimate mean
SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus
and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV
luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR \sim
(1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2
X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less
X-ray luminous and have Mdot/SFR \sim (0.2-0.4) x10^-3, comparable to z ~ 1-2
star-forming galaxies with similar mean X-ray luminosities. We estimate that a
periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the
star-forming galaxies onto the local MBH/M* relation.
We present results from a ~100 ks Chandra observation of the 2QZ Cluster
1004+00 structure at z = 2.23 (hereafter, 2QZ Clus). 2QZ Clus was originally
identified as an overdensity of four optically-selected QSOs at z = 2.23 within
a 15x15 arcmin^2 region. Narrow-band imaging in the near-IR revealed that the
structure contains an additional overdensity of 22 z = 2.23 Halpha-emitting
galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs. Our Chandra
observations reveal that 3 HAEs in addition to the 4 QSOs harbor powerfully
accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of
~(8-60) x 10^43 ergs/s and X-ray spectral slopes consistent with unobscured
AGN. Using a large comparison sample of 210 HAEs in Chandra-COSMOS (C-COSMOS),
we find suggestive evidence that the AGN fraction increases with local HAE
galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment
(a factor of ~2 times over the field), and after excluding optically-selected
QSOs, we find the AGN fraction is a factor of ~3.5^+3.8_-2.2 times higher than
C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra
data and Herschel SPIRE observations at 250 um, we respectively estimate mean
SMBH accretion rates (Mdot) and star-formation rates (SFRs) for the 2QZ Clus
and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked 2-10 keV
luminosity is QSO-like (~6-10 x 10^43 ergs/s), and the implied Mdot/SFR \sim
(1.6-3.2) x10^-3 is broadly consistent with the local MBH/M* relation and z ~ 2
X-ray selected AGN. The C-COSMOS HAEs are on average an order of magnitude less
X-ray luminous and have Mdot/SFR \sim (0.2-0.4) x10^-3, comparable to z ~ 1-2
star-forming galaxies with similar mean X-ray luminosities. We estimate that a
periodic QSO phase with duty cycle ~2-8% would be sufficient to bring the
star-forming galaxies onto the local MBH/M* relation.
Monday, January 14, 2013
Momentum dependent mean-field dynamics of compressed nuclear matter and neutron stars. (arXiv:1206.4821v2 [nucl-th] CROSS LISTED)
Momentum dependent mean-field dynamics of compressed nuclear matter and neutron stars. (arXiv:1206.4821v2 [nucl-th] CROSS LISTED):
Nuclear matter and compact neutron stars are studied in the framework of the
non-linear derivative (NLD) model which accounts for the momentum dependence of
relativistic mean-fields. The generalized form of the energy-momentum tensor is
derived which allows to consider different forms of the regulator functions in
the NLD Lagrangian. The thermodynamic consistency of the NLD model is
demonstrated for arbitrary choice of the regulator functions. The NLD approach
describes the bulk properties of the nuclear matter and compares well with
microscopic calculations and Dirac phenomenology. We further study the high
density domain of the nuclear equation of state (EoS) relevant for the matter
in $\beta$-equilibrium inside neutron stars. It is shown that the low density
constraints imposed on the nuclear EoS and by the momentum dependence of the
Schr\"odinger-equivalent optical potential lead to a maximum mass of the
neutron stars around $M \simeq 2 M_{\odot}$ which accommodates the observed
mass of the J1614-2230 millisecond radio pulsar.
Nuclear matter and compact neutron stars are studied in the framework of the
non-linear derivative (NLD) model which accounts for the momentum dependence of
relativistic mean-fields. The generalized form of the energy-momentum tensor is
derived which allows to consider different forms of the regulator functions in
the NLD Lagrangian. The thermodynamic consistency of the NLD model is
demonstrated for arbitrary choice of the regulator functions. The NLD approach
describes the bulk properties of the nuclear matter and compares well with
microscopic calculations and Dirac phenomenology. We further study the high
density domain of the nuclear equation of state (EoS) relevant for the matter
in $\beta$-equilibrium inside neutron stars. It is shown that the low density
constraints imposed on the nuclear EoS and by the momentum dependence of the
Schr\"odinger-equivalent optical potential lead to a maximum mass of the
neutron stars around $M \simeq 2 M_{\odot}$ which accommodates the observed
mass of the J1614-2230 millisecond radio pulsar.
Dense QCD and phenomenology of compact stars. (arXiv:1301.2675v1 [astro-ph.HE])
Dense QCD and phenomenology of compact stars. (arXiv:1301.2675v1 [astro-ph.HE]):
I discuss three topics in physics of massive (two solar-mass and larger)
neutron stars containing deconfined quark matter: (i) the equation of state of
deconfined dense quark matter and its color superconducting phases, (ii) the
thermal evolution of stars with quark cores, (iii) color-magnetic flux tubes in
type-II superconducting quark matter and their dynamics driven by Aharonov-Bohm
interactions with unpaired fermions.
I discuss three topics in physics of massive (two solar-mass and larger)
neutron stars containing deconfined quark matter: (i) the equation of state of
deconfined dense quark matter and its color superconducting phases, (ii) the
thermal evolution of stars with quark cores, (iii) color-magnetic flux tubes in
type-II superconducting quark matter and their dynamics driven by Aharonov-Bohm
interactions with unpaired fermions.
Structure of Spin Polarized Strange Quark Star in the Presence of Magnetic Field at Finite Temperature. (arXiv:1301.0899v1 [astro-ph.SR])
Structure of Spin Polarized Strange Quark Star in the Presence of Magnetic Field at Finite Temperature. (arXiv:1301.0899v1 [astro-ph.SR]):
In this paper, we have calculated the thermodynamic properties of spin
polarized strange quark matter at finite temperature in the presence of a
strong magnetic field using MIT bag model. We have also computed the equation
of state of spin polarized strange quark matter in the presence of strong
magnetic field and finally, using this equation of states we have investigated
the structure of spin polarized strange quark star at different temperatures
and magnetic fields.
In this paper, we have calculated the thermodynamic properties of spin
polarized strange quark matter at finite temperature in the presence of a
strong magnetic field using MIT bag model. We have also computed the equation
of state of spin polarized strange quark matter in the presence of strong
magnetic field and finally, using this equation of states we have investigated
the structure of spin polarized strange quark star at different temperatures
and magnetic fields.
Updated catalog of 132,684 galaxy clusters and evolution of brightest cluster galaxies. (arXiv:1301.0871v1 [astro-ph.CO])
Updated catalog of 132,684 galaxy clusters and evolution of brightest cluster galaxies. (arXiv:1301.0871v1 [astro-ph.CO]):
We identified 132,684 clusters in the redshift range of 0.05<z<0.8 from SDSS
DR8. The spectroscopic redshifts of 52,683 clusters have been included in the
catalog using SDSS DR9 data. We found that BCGs are more luminous in richer
clusters and at higher redshifts.
We identified 132,684 clusters in the redshift range of 0.05<z<0.8 from SDSS
DR8. The spectroscopic redshifts of 52,683 clusters have been included in the
catalog using SDSS DR9 data. We found that BCGs are more luminous in richer
clusters and at higher redshifts.
Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO])
Resolving The Generation of Starburst Winds in Galaxy Mergers. (arXiv:1301.0841v1 [astro-ph.CO]):
We study galaxy super-winds driven in major mergers, using pc-resolution
simulations with detailed models for stellar feedback that can
self-consistently follow the formation/destruction of GMCs and generation of
winds. The models include molecular cooling, star formation at high densities
in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and
radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky
Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in
all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind
mass-loading efficiency (outflow rate divided by SFR) is similar to that in
isolated galaxy counterparts of each merger: it depends more on global galaxy
properties (mass, size, escape velocity) than on the dynamical state of the
merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up
complex morphologies with overlapping, differently-oriented bubbles/shells at a
range of radii. The winds have complex velocity and phase structure, with
material at a range of speeds up to ~1000 km/s, and a mix of molecular,
ionized, and hot gas that depends on galaxy properties and different feedback
mechanisms. These simulations resolve a problem in some 'sub-grid' models,
where simple wind prescriptions can dramatically suppress merger-induced
starbursts. But despite large mass-loading factors (>~10) in the winds, the
peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration
does not act equally, so cold dense gas can still lose angular momentum and
form stars, while blowing out gas that would not have participated in the
starburst in the first place. Considerable wind material is not unbound, and
falls back on the disk at later times post-merger, leading to higher
post-starburst SFRs in the presence of stellar feedback. This may require AGN
feedback to explain galaxy quenching.
We study galaxy super-winds driven in major mergers, using pc-resolution
simulations with detailed models for stellar feedback that can
self-consistently follow the formation/destruction of GMCs and generation of
winds. The models include molecular cooling, star formation at high densities
in GMCs, and gas recycling and feedback from SNe (I&II), stellar winds, and
radiation pressure. We study mergers of systems from SMC-like dwarfs and Milky
Way analogues to z~2 starburst disks. Multi-phase super-winds are generated in
all passages, with outflow rates up to ~1000 M_sun/yr. However, the wind
mass-loading efficiency (outflow rate divided by SFR) is similar to that in
isolated galaxy counterparts of each merger: it depends more on global galaxy
properties (mass, size, escape velocity) than on the dynamical state of the
merger. Winds tend to be bi- or uni-polar, but multiple 'events' build up
complex morphologies with overlapping, differently-oriented bubbles/shells at a
range of radii. The winds have complex velocity and phase structure, with
material at a range of speeds up to ~1000 km/s, and a mix of molecular,
ionized, and hot gas that depends on galaxy properties and different feedback
mechanisms. These simulations resolve a problem in some 'sub-grid' models,
where simple wind prescriptions can dramatically suppress merger-induced
starbursts. But despite large mass-loading factors (>~10) in the winds, the
peak SFRs are comparable to those in 'no wind' simulations. Wind acceleration
does not act equally, so cold dense gas can still lose angular momentum and
form stars, while blowing out gas that would not have participated in the
starburst in the first place. Considerable wind material is not unbound, and
falls back on the disk at later times post-merger, leading to higher
post-starburst SFRs in the presence of stellar feedback. This may require AGN
feedback to explain galaxy quenching.
The mass and the radius of the neutron star in the transient low mass X-ray binary SAX J1748.9-2021. (arXiv:1301.0831v1 [astro-ph.HE])
The mass and the radius of the neutron star in the transient low mass X-ray binary SAX J1748.9-2021. (arXiv:1301.0831v1 [astro-ph.HE]):
We use time resolved spectroscopy of thermonuclear X-ray bursts observed from
SAX J1748.9-2021 to infer the mass and the radius of the neutron star in the
binary. Four X-ray bursts observed from the source with RXTE enable us to
measure the angular size and the Eddington limit on the neutron star surface.
Combined with a distance measurement to the globular cluster NGC 6440, in which
SAX J1748.9-2021 resides, we obtain two solutions for the neutron star radius
and mass, R = 8.18 +/- 1.62 km and M = 1.78 +/- 0.3 M_\sun or R = 10.93 +/-
2.09 km and M = 1.33 +/- 0.33 M_\sun.
We use time resolved spectroscopy of thermonuclear X-ray bursts observed from
SAX J1748.9-2021 to infer the mass and the radius of the neutron star in the
binary. Four X-ray bursts observed from the source with RXTE enable us to
measure the angular size and the Eddington limit on the neutron star surface.
Combined with a distance measurement to the globular cluster NGC 6440, in which
SAX J1748.9-2021 resides, we obtain two solutions for the neutron star radius
and mass, R = 8.18 +/- 1.62 km and M = 1.78 +/- 0.3 M_\sun or R = 10.93 +/-
2.09 km and M = 1.33 +/- 0.33 M_\sun.
ISM composition through X-ray spectroscopy of LMXBs. (arXiv:1301.1612v1 [astro-ph.GA])
ISM composition through X-ray spectroscopy of LMXBs. (arXiv:1301.1612v1 [astro-ph.GA]):
The diffuse interstellar medium (ISM) is an integral part of the evolution of
the entire Galaxy. Metals are produced by stars and their abundances are the
direct testimony of the history of stellar evolution. However, the interstellar
dust composition is not well known and the total abundances are yet to be
accurately determined. We probe ISM dust composition, total abundances, and
abundance gradients through the study of interstellar absorption features in
the high-resolution X-ray spectra of Galactic low-mass X-ray binaries (LMXBs).
We use high-quality grating spectra of nine LMXBs taken with XMM-Newton. We
measure the column densities of O, Ne, Mg, and Fe with an empirical model and
estimate the Galactic abundance gradients. The column densities of the neutral
gas species are in agreement with those found in the literature. Solids are a
significant reservoir of metals like oxygen and iron. Respectively, 15-25 % and
65-90 % of the total amount of O I and Fe I is found in dust. The dust amount
and mixture seem to be consistent along all the lines-of-sight (LOS). Our
estimates of abundance gradients and predictions of local interstellar
abundances are in agreement with those measured at longer wavelengths. Our work
shows that X-ray spectroscopy is a very powerful method to probe the ISM. For
instance, on a large scale the ISM appears to be chemically homogeneous showing
similar gas ionization ratios and dust mixtures. The agreement between the
abundances of the ISM and the stellar objects suggests that the local Galaxy is
also chemically homogeneous.
The diffuse interstellar medium (ISM) is an integral part of the evolution of
the entire Galaxy. Metals are produced by stars and their abundances are the
direct testimony of the history of stellar evolution. However, the interstellar
dust composition is not well known and the total abundances are yet to be
accurately determined. We probe ISM dust composition, total abundances, and
abundance gradients through the study of interstellar absorption features in
the high-resolution X-ray spectra of Galactic low-mass X-ray binaries (LMXBs).
We use high-quality grating spectra of nine LMXBs taken with XMM-Newton. We
measure the column densities of O, Ne, Mg, and Fe with an empirical model and
estimate the Galactic abundance gradients. The column densities of the neutral
gas species are in agreement with those found in the literature. Solids are a
significant reservoir of metals like oxygen and iron. Respectively, 15-25 % and
65-90 % of the total amount of O I and Fe I is found in dust. The dust amount
and mixture seem to be consistent along all the lines-of-sight (LOS). Our
estimates of abundance gradients and predictions of local interstellar
abundances are in agreement with those measured at longer wavelengths. Our work
shows that X-ray spectroscopy is a very powerful method to probe the ISM. For
instance, on a large scale the ISM appears to be chemically homogeneous showing
similar gas ionization ratios and dust mixtures. The agreement between the
abundances of the ISM and the stellar objects suggests that the local Galaxy is
also chemically homogeneous.
The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds. (arXiv:1301.1345v1 [astro-ph.CO])
The Milky Way halo as a QSO absorption-line system. New results from an HST/STIS absorption-line catalogue of Galactic high-velocity clouds. (arXiv:1301.1345v1 [astro-ph.CO]):
We use archival UV absorption-line data from HST/STIS to statistically
analyse the absorption characteristics of the high-velocity clouds (HVCs) in
the Galactic halo towards more than 40 extragalactic background sources. We
determine absorption covering fractions of low- and intermediate ions (OI, CII,
SiIII, MgII, FeII, SiIII, CIV, and SiIV) in the range fc = 0.20 - 0.70. For
detailed analysis we concentrate on SiII absorption components in HVCs, for
which we investigate the distribution of column densities, b-values, and radial
velocities. Combining information for SiII and MgII, and using a geometrical
HVC model we investigate the contribution of HVCs to the absorption cross
section of strong MgII absorbers in the local Universe. We estimate that the
Galactic HVCs would contribute on average ~52 % to the total strong MgII cross
section of the Milky Way, if our Galaxy were to be observed from an exterior
vantage point. We further estimate that the mean projected covering fraction of
strong MgII absorption in the Milky Way halo and disc from an exterior vantage
point is fc(sMgII) = 0.31 for a halo radius of R = 61 kpc. These numbers,
together with the observed number density of strong MgII absorbers at low
redshift, indicate that the contribution of infalling gas clouds (i.e., HVC
analogues) in the halos of Milky Way-type galaxies to the cross section of
strong MgII absorbers is <34 %. These findings are in line with the idea that
outflowing gas (e.g., produced by galactic winds) in the halos of more actively
star-forming galaxies dominate the absorption-cross section of strong MgII
absorbers in the local Universe.
We use archival UV absorption-line data from HST/STIS to statistically
analyse the absorption characteristics of the high-velocity clouds (HVCs) in
the Galactic halo towards more than 40 extragalactic background sources. We
determine absorption covering fractions of low- and intermediate ions (OI, CII,
SiIII, MgII, FeII, SiIII, CIV, and SiIV) in the range fc = 0.20 - 0.70. For
detailed analysis we concentrate on SiII absorption components in HVCs, for
which we investigate the distribution of column densities, b-values, and radial
velocities. Combining information for SiII and MgII, and using a geometrical
HVC model we investigate the contribution of HVCs to the absorption cross
section of strong MgII absorbers in the local Universe. We estimate that the
Galactic HVCs would contribute on average ~52 % to the total strong MgII cross
section of the Milky Way, if our Galaxy were to be observed from an exterior
vantage point. We further estimate that the mean projected covering fraction of
strong MgII absorption in the Milky Way halo and disc from an exterior vantage
point is fc(sMgII) = 0.31 for a halo radius of R = 61 kpc. These numbers,
together with the observed number density of strong MgII absorbers at low
redshift, indicate that the contribution of infalling gas clouds (i.e., HVC
analogues) in the halos of Milky Way-type galaxies to the cross section of
strong MgII absorbers is <34 %. These findings are in line with the idea that
outflowing gas (e.g., produced by galactic winds) in the halos of more actively
star-forming galaxies dominate the absorption-cross section of strong MgII
absorbers in the local Universe.
X-ray Polarization from Black Holes: GEMS Scientific White Paper. (arXiv:1301.1957v1 [astro-ph.HE])
X-ray Polarization from Black Holes: GEMS Scientific White Paper. (arXiv:1301.1957v1 [astro-ph.HE]):
We present here a summary of the scientific goals behind the Gravity and
Extreme Magnetism SMEX (GEMS) X-ray polarimetry mission's black hole (BH)
observing program. The primary targets can be divided into two classes:
stellar-mass galactic BHs in accreting binaries, and super-massive BHs in the
centers of active galactic nuclei (AGN). The stellar-mass BHs can in turn be
divided into various X-ray spectral states: thermal-dominant (disk), hard
(radio jet), and steep power-law (hot corona). These different spectral states
are thought to be generated by different accretion geometries and emission
mechanisms. X-ray polarization is an ideal tool for probing the geometry around
these BHs and revealing the specific properties of the accreting gas.
We present here a summary of the scientific goals behind the Gravity and
Extreme Magnetism SMEX (GEMS) X-ray polarimetry mission's black hole (BH)
observing program. The primary targets can be divided into two classes:
stellar-mass galactic BHs in accreting binaries, and super-massive BHs in the
centers of active galactic nuclei (AGN). The stellar-mass BHs can in turn be
divided into various X-ray spectral states: thermal-dominant (disk), hard
(radio jet), and steep power-law (hot corona). These different spectral states
are thought to be generated by different accretion geometries and emission
mechanisms. X-ray polarization is an ideal tool for probing the geometry around
these BHs and revealing the specific properties of the accreting gas.
Revealing the X-ray source in IRAS 13224-3809 through flux-dependent reverberation lags. (arXiv:1301.1924v1 [astro-ph.HE])
Revealing the X-ray source in IRAS 13224-3809 through flux-dependent reverberation lags. (arXiv:1301.1924v1 [astro-ph.HE]):
IRAS 13224-3809 was observed in 2011 for 500 ks with the XMM-Newton
observatory. We detect highly significant X-ray lags between soft (0.3 - 1 keV)
and hard (1.2 - 5 keV) energies. The hard band lags the soft at low frequencies
(i.e. hard lag), while the opposite (i.e. soft lag) is observed at high
frequencies. In this paper, we study the lag during flaring and quiescent
periods. We find that the frequency and absolute amplitude of the soft lag is
different during high-flux and low-flux periods. During the low flux intervals,
the soft lag is detected at higher frequencies and with smaller amplitude.
Assuming that the soft lag is associated with the light travel time between
primary and reprocessed emission, this behaviour suggests that the X-ray source
is more compact during low-flux intervals, and irradiates smaller radii of the
accretion disc (likely because of light bending effects). We continue with an
investigation of the lag dependence on energy, and find that isolating the
low-flux periods reveals a strong lag signature at the Fe K line energy,
similar to results found using 1.3 Ms of data on another well known Narrow-Line
Seyfert I galaxy, 1H0707-495.
IRAS 13224-3809 was observed in 2011 for 500 ks with the XMM-Newton
observatory. We detect highly significant X-ray lags between soft (0.3 - 1 keV)
and hard (1.2 - 5 keV) energies. The hard band lags the soft at low frequencies
(i.e. hard lag), while the opposite (i.e. soft lag) is observed at high
frequencies. In this paper, we study the lag during flaring and quiescent
periods. We find that the frequency and absolute amplitude of the soft lag is
different during high-flux and low-flux periods. During the low flux intervals,
the soft lag is detected at higher frequencies and with smaller amplitude.
Assuming that the soft lag is associated with the light travel time between
primary and reprocessed emission, this behaviour suggests that the X-ray source
is more compact during low-flux intervals, and irradiates smaller radii of the
accretion disc (likely because of light bending effects). We continue with an
investigation of the lag dependence on energy, and find that isolating the
low-flux periods reveals a strong lag signature at the Fe K line energy,
similar to results found using 1.3 Ms of data on another well known Narrow-Line
Seyfert I galaxy, 1H0707-495.
Bulk motion measurements in clusters of galaxies with ATHENA-like missions. (arXiv:1301.1852v1 [astro-ph.CO])
Bulk motion measurements in clusters of galaxies with ATHENA-like missions. (arXiv:1301.1852v1 [astro-ph.CO]):
The hierarchical formation of clusters of galaxies by accretion of material
releases gravitational energy which dissipates into the intracluster gas. The
process heats the material and generates gas turbulence and bulk motions and
thus kinetic pressure. Mapping the velocity fields of the moving subunits would
enable a new diagnostics tool for cluster formation studies and unbiased X-ray
mass estimates. The required spatially resolved high resolution spectroscopy is
not currently available. I demonstrate here the feasibility of detecting and
mapping the velocities of the bulk motions using the Doppler shift of the Fe
XXV K alpha line with the proposed ATHENA satellite.
The hierarchical formation of clusters of galaxies by accretion of material
releases gravitational energy which dissipates into the intracluster gas. The
process heats the material and generates gas turbulence and bulk motions and
thus kinetic pressure. Mapping the velocity fields of the moving subunits would
enable a new diagnostics tool for cluster formation studies and unbiased X-ray
mass estimates. The required spatially resolved high resolution spectroscopy is
not currently available. I demonstrate here the feasibility of detecting and
mapping the velocities of the bulk motions using the Doppler shift of the Fe
XXV K alpha line with the proposed ATHENA satellite.
The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra. (arXiv:1301.1847v1 [astro-ph.SR])
The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra. (arXiv:1301.1847v1 [astro-ph.SR]):
We analyze the high-resolution X-ray spectrum of the supergiant O-star delta
Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model,
and we examine its variability. The O-supergiant delta Ori was observed in the
wavelength range 5-175 Angstrom by the X-ray detector HRC-S in combination with
the grating LETG aboard Chandra. We studied the He-like ions in combination
with the UV-radiation field to determine local plasma temperatures and to
establish the distance of the X-ray emitting ions to the stellar surface. We
measured individual lines by means of Gaussian profiles, folded through the
response matrix, to obtain wavelengths, line fluxes, half widths at half
maximum (HWHM) and line shifts to characterize the plasma. We consider
multitemperature models in collisional ionization equilibrium (CIE) to
determine temperatures, emission measures, and abundances. Analysis of the
He-like triplets extended to N VI and C V implies ionization stratification
with the hottest plasma to be found within a few stellar radii 3R* (Mg XI) and
the coolest farther out, far beyond the acceleration zone, up to 49R* (N VI)
and 75R* (C V). The observed temperatures cover a range from about 0.1 to 0.7
keV, i.e., 1-8 MK. The X-ray luminosity L is about 1.5 x 10e+32 erg/s in the
range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km/s
have been determined.
We analyze the high-resolution X-ray spectrum of the supergiant O-star delta
Orionis (O9.5II) with line ratios of He-like ions and a thermal plasma model,
and we examine its variability. The O-supergiant delta Ori was observed in the
wavelength range 5-175 Angstrom by the X-ray detector HRC-S in combination with
the grating LETG aboard Chandra. We studied the He-like ions in combination
with the UV-radiation field to determine local plasma temperatures and to
establish the distance of the X-ray emitting ions to the stellar surface. We
measured individual lines by means of Gaussian profiles, folded through the
response matrix, to obtain wavelengths, line fluxes, half widths at half
maximum (HWHM) and line shifts to characterize the plasma. We consider
multitemperature models in collisional ionization equilibrium (CIE) to
determine temperatures, emission measures, and abundances. Analysis of the
He-like triplets extended to N VI and C V implies ionization stratification
with the hottest plasma to be found within a few stellar radii 3R* (Mg XI) and
the coolest farther out, far beyond the acceleration zone, up to 49R* (N VI)
and 75R* (C V). The observed temperatures cover a range from about 0.1 to 0.7
keV, i.e., 1-8 MK. The X-ray luminosity L is about 1.5 x 10e+32 erg/s in the
range from 0.07 to 3 keV covered by LETGS. Velocity widths of about 1040 km/s
have been determined.
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin. (arXiv:1301.1800v1 [astro-ph.CO])
X-ray emission from the Ultramassive Black Hole candidate NGC1277: implications and speculation on its origin. (arXiv:1301.1800v1 [astro-ph.CO]):
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.
We study the X-ray emission from NGC1277, a galaxy in the core of the Perseus
cluster, for which van den Bosch et al. have recently claimed the presence of
an UltraMassive Black Hole (UMBH) of mass 1.7 times 10^10 Msun, unless the IMF
of the stars in the stellar bulge is extremely bottom heavy. The X-rays
originate in a power-law component of luminosity 1.3 times 10^40 erg/s embedded
in a 1 keV thermal minicorona which has a half-light radius of about 360 pc,
typical of many early-type galaxies in rich clusters of galaxies. If Bondi
accretion operated onto the UMBH from the minicorona with a radiative
efficiency of 10 per cent, then the object would appear as a quasar with
luminosity 10^46 erg/s, a factor of almost 10^6 times higher than observed. The
accretion flow must be highly radiatively inefficient, similar to past results
on M87 and NGC3115. The UMBH in NGC1277 is definitely not undergoing any
significant growth at the present epoch. We note that there are 3 UMBH
candidates in the Perseus cluster and that the inferred present mean mass
density in UMBH could be 10^5 Msun/Mpc^3, which is 20 to 30 per cent of the
estimated mean mass density of all black holes. We speculate on the implied
growth of UMBH and their hosts, and discuss the possibiity that extreme AGN
feedback could make all UMBH host galaxies have low stellar masses at redshifts
around 3. Only those which end up at the centres of groups and clusters later
accrete large stellar envelopes and become Brightest Cluster Galaxies. NGC1277
and the other Perseus core UMBH, NGC1270, have not however been able to gather
more stars or gas owing to their rapid orbital motion in the cluster core.
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1. (arXiv:1301.1689v1 [astro-ph.CO])
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1. (arXiv:1301.1689v1 [astro-ph.CO]):
We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion rate
(the rate of supermassive black hole growth scaled relative to the host stellar
mass). Our model is based on measurements indicating that the specific
accretion rate distribution is a universal function across a wide range of host
stellar mass with slope gamma_1=0.65 and an overall normalization that evolves
strongly with redshift. We test several simple assumptions to extend this model
to high specific accretion rates (beyond the measurements) and compare the
predictions for the XLF with the observed data. We find good agreement with a
model that allows for a break in the specific accretion rate distribution at a
point corresponding to the Eddington limit, with a steep power-law tail to
super-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convert between
specific accretion rate and Eddington ratio by assuming a scaling between black
hole mass and host stellar mass with an intrinsic scatter of +/-0.38 dex. Our
results show that samples of low luminosity AGNs are dominated by moderately
massive galaxies (M* ~ 10^{10-11} M_sun) growing with a wide range of accretion
rates -- a consequence of the shape of the galaxy stellar mass function rather
than a preference for AGN activity at a particular stellar mass. The observed
population of the most luminous AGN may be severely skewed to the most extreme
sources with elevated black hole masses relative to their host galaxies and in
rare phases of very rapid accretion.
We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion rate
(the rate of supermassive black hole growth scaled relative to the host stellar
mass). Our model is based on measurements indicating that the specific
accretion rate distribution is a universal function across a wide range of host
stellar mass with slope gamma_1=0.65 and an overall normalization that evolves
strongly with redshift. We test several simple assumptions to extend this model
to high specific accretion rates (beyond the measurements) and compare the
predictions for the XLF with the observed data. We find good agreement with a
model that allows for a break in the specific accretion rate distribution at a
point corresponding to the Eddington limit, with a steep power-law tail to
super-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convert between
specific accretion rate and Eddington ratio by assuming a scaling between black
hole mass and host stellar mass with an intrinsic scatter of +/-0.38 dex. Our
results show that samples of low luminosity AGNs are dominated by moderately
massive galaxies (M* ~ 10^{10-11} M_sun) growing with a wide range of accretion
rates -- a consequence of the shape of the galaxy stellar mass function rather
than a preference for AGN activity at a particular stellar mass. The observed
population of the most luminous AGN may be severely skewed to the most extreme
sources with elevated black hole masses relative to their host galaxies and in
rare phases of very rapid accretion.
Observations of Feedback from Radio-Quiet Quasars: I. Extents and Morphologies of Ionized Gas Nebulae. (arXiv:1301.1677v1 [astro-ph.CO])
Observations of Feedback from Radio-Quiet Quasars: I. Extents and Morphologies of Ionized Gas Nebulae. (arXiv:1301.1677v1 [astro-ph.CO]):
Black hole feedback -- the strong interaction between the energy output of
supermassive black holes and their surrounding environments -- is routinely
invoked to explain the absence of overly luminous galaxies, the black hole vs.
bulge correlations and the similarity of black hole accretion and star
formation histories. Yet direct probes of this process in action are scarce and
limited to small samples of active nuclei. We present Gemini IFU observations
of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ)
quasars at z~0.5. We detect extended ionized gas nebulae via [O III]5007
emission in every case, with a mean diameter of 28 kpc. These nebulae are
nearly perfectly round. The regular morphologies of nebulae around RQ quasars
are in striking contrast with lumpy or elongated nebulae seen around radio
galaxies at low and high redshifts. We present the uniformly measured
size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and
type 2 quasars spanning 6 orders of magnitude in luminosity and confirm the
flat slope of the correlation (R ~ L^{0.25+/-0.02}). We find a universal
behavior of the [O III]/H-beta ratio in our entire RQ quasar sample: it
persists at a constant value (~10) in the central regions, until reaching a
"break" isophotal radius ranging from 4 to 11 kpc where it starts to decrease.
We propose a model of clumpy nebulae in which clouds that produce line emission
transition from being ionization-bounded at small distances from the quasar to
being matter-bounded in the outer parts of the nebula, which qualitatively
explains the observed line ratio and surface brightness profiles. It is
striking that we see such smooth and round large-scale gas nebulosities in this
sample, which are inconsistent with illuminated merger debris and which we
suggest may be the signature of accretion energy from the nucleus reaching gas
at large scales.
Black hole feedback -- the strong interaction between the energy output of
supermassive black holes and their surrounding environments -- is routinely
invoked to explain the absence of overly luminous galaxies, the black hole vs.
bulge correlations and the similarity of black hole accretion and star
formation histories. Yet direct probes of this process in action are scarce and
limited to small samples of active nuclei. We present Gemini IFU observations
of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ)
quasars at z~0.5. We detect extended ionized gas nebulae via [O III]5007
emission in every case, with a mean diameter of 28 kpc. These nebulae are
nearly perfectly round. The regular morphologies of nebulae around RQ quasars
are in striking contrast with lumpy or elongated nebulae seen around radio
galaxies at low and high redshifts. We present the uniformly measured
size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and
type 2 quasars spanning 6 orders of magnitude in luminosity and confirm the
flat slope of the correlation (R ~ L^{0.25+/-0.02}). We find a universal
behavior of the [O III]/H-beta ratio in our entire RQ quasar sample: it
persists at a constant value (~10) in the central regions, until reaching a
"break" isophotal radius ranging from 4 to 11 kpc where it starts to decrease.
We propose a model of clumpy nebulae in which clouds that produce line emission
transition from being ionization-bounded at small distances from the quasar to
being matter-bounded in the outer parts of the nebula, which qualitatively
explains the observed line ratio and surface brightness profiles. It is
striking that we see such smooth and round large-scale gas nebulosities in this
sample, which are inconsistent with illuminated merger debris and which we
suggest may be the signature of accretion energy from the nucleus reaching gas
at large scales.
The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA])
The Atlas3D project - XIX. The hot-gas content of early-type galaxies: fast versus slow rotators. (arXiv:1301.2589v1 [astro-ph.GA]):
For early-type galaxies, the ability to sustain a corona of hot, X-ray
emitting gas could have played a key role in quenching their star-formation
history. Yet, it is still unclear what drives the precise amount of hot gas
around these galaxies. By combining photometric and spectroscopic measurements
for the early-type galaxies observed during the Atlas3D integral-field survey
with measurements of their X-ray luminosity based on X-ray data of both low and
high spatial resolution we conclude that the hot-gas content of early-type
galaxies can depend on their dynamical structure. Specifically, whereas slow
rotators generally have X-ray halos with luminosity L_X,gas and temperature T
values that are in line with what is expected if the hot-gas emission is
sustained by the thermalisaton of the kinetic energy carried by the
stellar-mass loss material, fast rotators tend to display L_X,gas values that
fall consistently below the prediction of this model, with similar T values
that do not scale with the stellar kinetic energy as observed in the case of
slow rotators. Considering that fast rotators are likely to be intrinsically
flatter than slow rotators, and that the few L_X,gas-deficient slow rotators
also happen to be relatively flat, the observed L_X,gas deficiency in these
objects would support the hypothesis whereby flatter galaxies have a harder
time in retaining their hot gas. We discuss the implications that a different
hot-gas content could have on the fate of both acquired and internally-produced
gaseous material, considering in particular how the L_X,gas deficiency of fast
rotators would make them more capable to recycle the stellar-mass loss material
into new stars than slow rotators. This is consistent with the finding that
molecular gas and young stars are detected only in fast rotators in the Atlas3D
sample, and that fast rotators tend to dustier than slow rotators. [Abridged]
For early-type galaxies, the ability to sustain a corona of hot, X-ray
emitting gas could have played a key role in quenching their star-formation
history. Yet, it is still unclear what drives the precise amount of hot gas
around these galaxies. By combining photometric and spectroscopic measurements
for the early-type galaxies observed during the Atlas3D integral-field survey
with measurements of their X-ray luminosity based on X-ray data of both low and
high spatial resolution we conclude that the hot-gas content of early-type
galaxies can depend on their dynamical structure. Specifically, whereas slow
rotators generally have X-ray halos with luminosity L_X,gas and temperature T
values that are in line with what is expected if the hot-gas emission is
sustained by the thermalisaton of the kinetic energy carried by the
stellar-mass loss material, fast rotators tend to display L_X,gas values that
fall consistently below the prediction of this model, with similar T values
that do not scale with the stellar kinetic energy as observed in the case of
slow rotators. Considering that fast rotators are likely to be intrinsically
flatter than slow rotators, and that the few L_X,gas-deficient slow rotators
also happen to be relatively flat, the observed L_X,gas deficiency in these
objects would support the hypothesis whereby flatter galaxies have a harder
time in retaining their hot gas. We discuss the implications that a different
hot-gas content could have on the fate of both acquired and internally-produced
gaseous material, considering in particular how the L_X,gas deficiency of fast
rotators would make them more capable to recycle the stellar-mass loss material
into new stars than slow rotators. This is consistent with the finding that
molecular gas and young stars are detected only in fast rotators in the Atlas3D
sample, and that fast rotators tend to dustier than slow rotators. [Abridged]
Unified description of dense matter in neutron stars and magnetars. (arXiv:1301.2438v1 [astro-ph.HE])
Unified description of dense matter in neutron stars and magnetars. (arXiv:1301.2438v1 [astro-ph.HE]):
We have recently developed a set of equations of state based on the nuclear
energy density functional theory providing a unified description of the
different regions constituting the interior of neutron stars and magnetars. The
nuclear functionals, which were constructed from generalized Skyrme effective
nucleon-nucleon interactions, yield not only an excellent fit to essentially
all experimental atomic mass data but were also constrained to reproduce the
neutron-matter equation of state as obtained from realistic many-body
calculations.
We have recently developed a set of equations of state based on the nuclear
energy density functional theory providing a unified description of the
different regions constituting the interior of neutron stars and magnetars. The
nuclear functionals, which were constructed from generalized Skyrme effective
nucleon-nucleon interactions, yield not only an excellent fit to essentially
all experimental atomic mass data but were also constrained to reproduce the
neutron-matter equation of state as obtained from realistic many-body
calculations.
Early Thermal X-ray Emission from Long Gamma-ray Bursts and Their Circumstellar Environments. (arXiv:1301.2421v1 [astro-ph.HE])
Early Thermal X-ray Emission from Long Gamma-ray Bursts and Their Circumstellar Environments. (arXiv:1301.2421v1 [astro-ph.HE]):
We performed a series of hydrodynamical calculations of an ultra-relativistic
jet propagating through a massive star and the circumstellar matter to
investigate the interaction between the ejecta and the circumstellar matter. We
succeed in distinguishing two qualitatively different cases in which the ejecta
are shocked and adiabatically cool. To examine whether the cocoon expanding at
subrelativistic speeds emits any observable signal, we calculate expected
photospheric emission from the cocoon. It is found that the emission can
explain early thermal X-ray emission recently found in some long gamma-ray
bursts. The result implies that the difference of the circumstellar environment
of long gamma-ray bursts can be probed by observing their early thermal X-ray
emission.
We performed a series of hydrodynamical calculations of an ultra-relativistic
jet propagating through a massive star and the circumstellar matter to
investigate the interaction between the ejecta and the circumstellar matter. We
succeed in distinguishing two qualitatively different cases in which the ejecta
are shocked and adiabatically cool. To examine whether the cocoon expanding at
subrelativistic speeds emits any observable signal, we calculate expected
photospheric emission from the cocoon. It is found that the emission can
explain early thermal X-ray emission recently found in some long gamma-ray
bursts. The result implies that the difference of the circumstellar environment
of long gamma-ray bursts can be probed by observing their early thermal X-ray
emission.
A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO])
A comparative analysis of virial black-hole mass estimates of moderate-luminosity active galactic nuclei using Subaru/FMOS. (arXiv:1301.2332v1 [astro-ph.CO]):
We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.
We present an analysis of broad emission lines observed in
moderate-luminosity active galactic nuclei (AGNs), typical of those found in
X-ray surveys of deep fields, with the aim to test the validity of single-epoch
virial black hole mass estimates. We have acquired near-infrared (NIR) spectra
of AGNs up to z ~ 1.8 in the COSMOS and Extended Chandra Deep Field-South
Survey, with the Fiber Multi-Object Spectrograph (FMOS) mounted on the Subaru
Telescope. These low-resolution NIR spectra provide a significant detection of
the broad Halpha line that has been shown to be a reliable probe of black hole
mass at low redshift. Our sample has existing optical spectroscopy which
provides a detection of MgII, a broad emission line typically used for black
hole mass estimation at z > 1. We carry out a spectral-line fitting procedure
using both Halpha and MgII to determine the virial velocity of gas in the broad
line region, the monochromatic continuum luminosity at 3000 A, and the total
Halpha line luminosity. With a sample of 43 AGNs spanning a range of two
decades in luminosity (i.e., L ~ 10^44-46 ergs/s), we find a tight correlation
between the continuum and line luminosity with a distribution characterized by
<log(L_3000/L_Halpha)> = 1.52 and a dispersion sigma = 0.16. There is also a
close one-to-one relationship between the FWHM of Halpha and of MgII up to
10000 km/s with a dispersion of 0.14 in the distribution of the logarithm of
their ratios. Both of these then lead to there being very good agreement
between Halpha- and MgII-based masses over a wide range in black hole mass
(i.e., M_BH ~ 10^7-9 M_sun). We do find a small offset in MgII-based masses,
relative to those based on Halpha, of +0.17 dex and a dispersion sigma = 0.32.
In general, these results demonstrate that local scaling relations, using MgII
or Halpha, are applicable for AGN at moderate luminosities and up to z ~ 2.
A Chandra X-ray study of the interacting binaries in the old open cluster NGC6791. (arXiv:1301.2331v1 [astro-ph.HE])
A Chandra X-ray study of the interacting binaries in the old open cluster NGC6791. (arXiv:1301.2331v1 [astro-ph.HE]):
We present the first X-ray study of NGC6791, one of the oldest open clusters
known (8 Gyr). Our Chandra observation is aimed at uncovering the population of
close interacting binaries down to Lx ~ 1e30 erg/s (0.3-7 keV). We detect 86
sources within 8 arcmin of the cluster center, including 59 inside the
half-mass radius. We identify twenty sources with proper-motion cluster
members, which are a mix of cataclysmic variables (CVs), active binaries (ABs),
and binaries containing sub-subgiants. With follow-up optical spectroscopy we
confirm the nature of one CV. We discover one new, X-ray variable candidate CV
with Balmer and HeII emission lines in its optical spectrum; this is the first
X-ray--selected CV confirmed in an open cluster. The number of CVs per unit
mass is consistent with the field, suggesting that the 3-4 CVs observed in
NGC6791 are primordial. We compare the X-ray properties of NGC6791 with those
of a few old open (NGC6819, M67) and globular clusters (47Tuc, NGC6397). It is
puzzling that the number of ABs brighter than 1e30 erg/s normalized by cluster
mass is lower in NGC6791 than in M67 by a factor ~3 to 7. CVs, ABs, and
sub-subgiants brighter than 1e30 erg/s are under-represented per unit mass in
the globular clusters compared to the oldest open clusters, and this accounts
for the lower total X-ray luminosity per unit mass of the former. This
indicates that the net effect of dynamical encounters may be the destruction of
even some of the hardest (i.e. X-ray--emitting) binaries.
We present the first X-ray study of NGC6791, one of the oldest open clusters
known (8 Gyr). Our Chandra observation is aimed at uncovering the population of
close interacting binaries down to Lx ~ 1e30 erg/s (0.3-7 keV). We detect 86
sources within 8 arcmin of the cluster center, including 59 inside the
half-mass radius. We identify twenty sources with proper-motion cluster
members, which are a mix of cataclysmic variables (CVs), active binaries (ABs),
and binaries containing sub-subgiants. With follow-up optical spectroscopy we
confirm the nature of one CV. We discover one new, X-ray variable candidate CV
with Balmer and HeII emission lines in its optical spectrum; this is the first
X-ray--selected CV confirmed in an open cluster. The number of CVs per unit
mass is consistent with the field, suggesting that the 3-4 CVs observed in
NGC6791 are primordial. We compare the X-ray properties of NGC6791 with those
of a few old open (NGC6819, M67) and globular clusters (47Tuc, NGC6397). It is
puzzling that the number of ABs brighter than 1e30 erg/s normalized by cluster
mass is lower in NGC6791 than in M67 by a factor ~3 to 7. CVs, ABs, and
sub-subgiants brighter than 1e30 erg/s are under-represented per unit mass in
the globular clusters compared to the oldest open clusters, and this accounts
for the lower total X-ray luminosity per unit mass of the former. This
indicates that the net effect of dynamical encounters may be the destruction of
even some of the hardest (i.e. X-ray--emitting) binaries.
Thursday, January 3, 2013
Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field. (arXiv:1301.0544v1 [nucl-th])
Finite temperature effects on anisotropic pressure and equation of state of dense neutron matter in an ultrastrong magnetic field. (arXiv:1301.0544v1 [nucl-th]):
Spin polarized states in dense neutron matter with recently developed Skyrme
effective interaction (BSk20 parametrization) are considered in the magnetic
fields $H$ up to $10^{20}$ G at finite temperature. In a strong magnetic field,
the total pressure in neutron matter is anisotropic, and the difference between
the pressures parallel and perpendicular to the field direction becomes
significant at $H>H_{th}\sim10^{18}$ G. The longitudinal pressure decreases
with the magnetic field and vanishes in the critical field
$10^{18}<H_c\lesssim10^{19}$ G, resulting in the longitudinal instability of
neutron matter. With increasing the temperature, the threshold $H_{th}$ and
critical $H_c$ magnetic fields also increase. The appearance of the
longitudinal instability prevents the formation of a fully spin polarized state
in neutron matter and only the states with moderate spin polarization are
accessible. The anisotropic equation of state is determined at densities and
temperatures relevant for the interiors of magnetars. The entropy of strongly
magnetized neutron matter turns out to be larger than the entropy of the
nonpolarized matter. This is caused by some specific details in the dependence
of the entropy on the effective masses of neutrons with spin up and spin down
in a polarized state.
Spin polarized states in dense neutron matter with recently developed Skyrme
effective interaction (BSk20 parametrization) are considered in the magnetic
fields $H$ up to $10^{20}$ G at finite temperature. In a strong magnetic field,
the total pressure in neutron matter is anisotropic, and the difference between
the pressures parallel and perpendicular to the field direction becomes
significant at $H>H_{th}\sim10^{18}$ G. The longitudinal pressure decreases
with the magnetic field and vanishes in the critical field
$10^{18}<H_c\lesssim10^{19}$ G, resulting in the longitudinal instability of
neutron matter. With increasing the temperature, the threshold $H_{th}$ and
critical $H_c$ magnetic fields also increase. The appearance of the
longitudinal instability prevents the formation of a fully spin polarized state
in neutron matter and only the states with moderate spin polarization are
accessible. The anisotropic equation of state is determined at densities and
temperatures relevant for the interiors of magnetars. The entropy of strongly
magnetized neutron matter turns out to be larger than the entropy of the
nonpolarized matter. This is caused by some specific details in the dependence
of the entropy on the effective masses of neutrons with spin up and spin down
in a polarized state.
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