The Bimodal Metallicity Distribution of the Cool Circumgalactic Medium at z<1. (arXiv:1302.5424v1 [astro-ph.CO]):
We assess the metal content of the circumgalactic medium (CGM) about galaxies
at z<1 using an HI-selected sample of 27 Lyman limit systems (LLS, defined here
as absorbers with 16.2\lesssimlog N(HI)\lesssim 18.5 observed in absorption
against background QSOs by the Cosmic Origins Spectrograph on-board the {Hubble
Space Telescope. The N(HI) selection avoids metallicity biases inherent in many
previous studies of the low-redshift CGM. We compare the column densities of
weakly ionized metal species (e.g., OII, CII, MgII) to N(HI) in the strongest
HI component of each absorber. We find that the metallicity distribution of the
LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches
peaking at [X/H]simeq1.6 and -0.4 (2.5% and 40% solar metallicities). The cool
CGM probed by these LLS is predominantly ionized. The metal-rich branch of the
population likely traces winds, recycled outflows, and tidally stripped gas;
the metal-poor branch has properties consistent with cold accretion streams
thought to be a major source of fresh gas for star forming galaxies. Both
branches have a nearly equal number of absorbers. Our results thus demonstrate
there is a significant mass of previously-undiscovered cold, metal-poor gas in
the CGM of z<1 galaxies.
Monday, February 25, 2013
A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO])
A Comparative Study of AGN Feedback Algorithms. (arXiv:1302.5420v1 [astro-ph.CO]):
Modelling AGN feedback in numerical simulations is both technically and
theoretically challenging, with numerous approaches having been published in
the literature. We present a study of five distinct approaches to modelling AGN
feedback within gravitohydrodynamic simulations of major mergers of Milky
Way-sized galaxies. To constrain differences to only be between AGN feedback
models, all simulations start from the same initial conditions and use the same
star formation algorithm. Most AGN feedback algorithms have five key aspects:
black hole accretion rate, energy feedback rate and method, particle accretion
algorithm, black hole advection algorithm, and black hole merger algorithm. All
models follow different accretion histories, with accretion rates that differ
by up to three orders of magnitude at any given time. We consider models with
either thermal or kinetic feedback, with the associated energy deposited
locally around the black hole. Each feedback algorithm modifies the gas
properties near the black hole to different extents. The particle accretion
algorithms usually (but not always) maintain good agreement between the mass
accreted by \dot{M} dt and the mass of gas particles removed from the
simulation. The black hole advection algorithms dampen inappropriate dragging
of the black holes by two-body interactions. Advecting the black hole a limited
distance based upon local mass distributions has many desirably properties. The
black holes merge when given criteria are met, and we find a range of merger
times for different criteria. Using the M_{BH}-\sigma relation as a diagnostic
of the remnants yields three models that lie within the one-sigma scatter of
the observed relation and two that fall below it. The wide variation in
accretion behaviours of the models reinforces the fact that there remains much
to be learnt about the evolution of galactic nuclei. (abridged)
Modelling AGN feedback in numerical simulations is both technically and
theoretically challenging, with numerous approaches having been published in
the literature. We present a study of five distinct approaches to modelling AGN
feedback within gravitohydrodynamic simulations of major mergers of Milky
Way-sized galaxies. To constrain differences to only be between AGN feedback
models, all simulations start from the same initial conditions and use the same
star formation algorithm. Most AGN feedback algorithms have five key aspects:
black hole accretion rate, energy feedback rate and method, particle accretion
algorithm, black hole advection algorithm, and black hole merger algorithm. All
models follow different accretion histories, with accretion rates that differ
by up to three orders of magnitude at any given time. We consider models with
either thermal or kinetic feedback, with the associated energy deposited
locally around the black hole. Each feedback algorithm modifies the gas
properties near the black hole to different extents. The particle accretion
algorithms usually (but not always) maintain good agreement between the mass
accreted by \dot{M} dt and the mass of gas particles removed from the
simulation. The black hole advection algorithms dampen inappropriate dragging
of the black holes by two-body interactions. Advecting the black hole a limited
distance based upon local mass distributions has many desirably properties. The
black holes merge when given criteria are met, and we find a range of merger
times for different criteria. Using the M_{BH}-\sigma relation as a diagnostic
of the remnants yields three models that lie within the one-sigma scatter of
the observed relation and two that fall below it. The wide variation in
accretion behaviours of the models reinforces the fact that there remains much
to be learnt about the evolution of galactic nuclei. (abridged)
Saturday, February 23, 2013
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO])
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO]):
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
Monday, February 18, 2013
Thermodynamics of the Coma Cluster Outskirts. (arXiv:1302.4140v1 [astro-ph.CO])
Thermodynamics of the Coma Cluster Outskirts. (arXiv:1302.4140v1 [astro-ph.CO]):
We present results from a large mosaic of Suzaku observations of the Coma
Cluster, focusing on the thermodynamic properties of the ICM on large scales.
The measured temperature and X-ray brightness profiles are similar along four
relatively undisturbed azimuths probed, with the temperature decreasing from
~8.5 keV at the cluster center to ~2 keV at 2 Mpc. The SW merger boosts the
surface brightness, allowing us to detect X-ray emission out to 2.5 Mpc along
this fifth direction. The X-ray image also reveals two arc-shaped regions with
excess surface brightness towards the east and west of the main cluster core.
These regions appear over-pressured and most likely originate from merger
induced large scale supersonic gas motions. The azimuthally averaged
temperature profile, as well as the deprojected density and pressure profiles
towards the E and NW, all show a sharp drop consistent with an outward
propagating shock front located at the outermost edge of the giant radio halo
observed at 352 MHz with the WSRT and which may be powering this radio
emission. The shape of the entropy profiles along the relatively relaxed E and
NW directions at large radii is consistent with the average profiles of
evolved, well formed cool core clusters, suggesting similar accretion
histories. Our data indicate a flat metal abundance profile at about 0.3 of the
Solar value out to almost the virial radius of Coma, which would favor galactic
winds over ram-pressure stripping as the dominant enrichment mechanism in the
ICM.
We present results from a large mosaic of Suzaku observations of the Coma
Cluster, focusing on the thermodynamic properties of the ICM on large scales.
The measured temperature and X-ray brightness profiles are similar along four
relatively undisturbed azimuths probed, with the temperature decreasing from
~8.5 keV at the cluster center to ~2 keV at 2 Mpc. The SW merger boosts the
surface brightness, allowing us to detect X-ray emission out to 2.5 Mpc along
this fifth direction. The X-ray image also reveals two arc-shaped regions with
excess surface brightness towards the east and west of the main cluster core.
These regions appear over-pressured and most likely originate from merger
induced large scale supersonic gas motions. The azimuthally averaged
temperature profile, as well as the deprojected density and pressure profiles
towards the E and NW, all show a sharp drop consistent with an outward
propagating shock front located at the outermost edge of the giant radio halo
observed at 352 MHz with the WSRT and which may be powering this radio
emission. The shape of the entropy profiles along the relatively relaxed E and
NW directions at large radii is consistent with the average profiles of
evolved, well formed cool core clusters, suggesting similar accretion
histories. Our data indicate a flat metal abundance profile at about 0.3 of the
Solar value out to almost the virial radius of Coma, which would favor galactic
winds over ram-pressure stripping as the dominant enrichment mechanism in the
ICM.
Sunday, February 17, 2013
PRIMUS: Infrared and X-ray AGN Selection Techniques at 0.2<z<1.2. (arXiv:1302.2920v1 [astro-ph.CO])
PRIMUS: Infrared and X-ray AGN Selection Techniques at 0.2<z<1.2. (arXiv:1302.2920v1 [astro-ph.CO]):
We present a study of Spitzer/IRAC and X-ray active galactic nuclei (AGNs)
selection techniques in order to quantify the overlap, uniqueness,
contamination, and completeness of each. We investigate how the overlap and
possible contamination of the samples depends on the IR and X-ray depths. We
use Spitzer/IRAC imaging, Chandra and XMM X-ray imaging, and PRism MUlti-object
Survey (PRIMUS) spectroscopic redshifts to construct galaxy and AGN samples at
0.2<z<1.2 over 8 deg^2. We construct samples over a wide range of IRAC flux
limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare
IR-AGN samples defined using the IRAC color selection of Stern et al. and
Donley et al. with X-ray detected AGN samples. For roughly similar depth IR and
X-ray surveys, we find that ~75% of IR-AGN are identified as X-ray AGN. This
fraction increases to ~90% when comparing against the deepest X-ray data,
indicating that only ~10% of IR-selected AGN may be heavily obscured. The
IR-AGN selection proposed by Stern et al. suffers from contamination by
star-forming galaxies at various redshifts when using deeper IR data, though
the selection technique works well for shallow IR data. While similar overall,
the IR-AGN samples preferentially contain more luminous AGN, while the X-ray
AGN samples preferentially contain lower specific accretion rate AGN, where the
host galaxy light dominates at IR wavelengths. The host galaxy populations of
the IR and X-ray AGN samples have similar restframe colors and stellar masses;
both selections identify AGN in blue, star-forming and red, quiescent galaxies.
We present a study of Spitzer/IRAC and X-ray active galactic nuclei (AGNs)
selection techniques in order to quantify the overlap, uniqueness,
contamination, and completeness of each. We investigate how the overlap and
possible contamination of the samples depends on the IR and X-ray depths. We
use Spitzer/IRAC imaging, Chandra and XMM X-ray imaging, and PRism MUlti-object
Survey (PRIMUS) spectroscopic redshifts to construct galaxy and AGN samples at
0.2<z<1.2 over 8 deg^2. We construct samples over a wide range of IRAC flux
limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare
IR-AGN samples defined using the IRAC color selection of Stern et al. and
Donley et al. with X-ray detected AGN samples. For roughly similar depth IR and
X-ray surveys, we find that ~75% of IR-AGN are identified as X-ray AGN. This
fraction increases to ~90% when comparing against the deepest X-ray data,
indicating that only ~10% of IR-selected AGN may be heavily obscured. The
IR-AGN selection proposed by Stern et al. suffers from contamination by
star-forming galaxies at various redshifts when using deeper IR data, though
the selection technique works well for shallow IR data. While similar overall,
the IR-AGN samples preferentially contain more luminous AGN, while the X-ray
AGN samples preferentially contain lower specific accretion rate AGN, where the
host galaxy light dominates at IR wavelengths. The host galaxy populations of
the IR and X-ray AGN samples have similar restframe colors and stellar masses;
both selections identify AGN in blue, star-forming and red, quiescent galaxies.
Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?. (arXiv:1302.3442v1 [astro-ph.HE])
Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?. (arXiv:1302.3442v1 [astro-ph.HE]):
It is believed that jets emerging from blazars (Flat Spectrum Radio Quasars
(FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually
exhibit lower luminosity and harder power law spectra at gamma-ray energies
than FSRQs. It was argued previously that the difference in accretion rates is
mainly responsible for the large observed luminosity mismatch between them.
However, when intrinsic luminosities are derived by correcting for beaming
effects, this mismatch is significantly reduced. We show that spin plays an
important role to reveal the dichotomy of luminosity distributions between BL
Lacs and FSRQs, suggesting BL Lacs to be low luminous and slow rotators
compared to FSRQs.
It is believed that jets emerging from blazars (Flat Spectrum Radio Quasars
(FSRQs) and BL Lacs) are almost aligned to the line-of-sight. BL Lacs usually
exhibit lower luminosity and harder power law spectra at gamma-ray energies
than FSRQs. It was argued previously that the difference in accretion rates is
mainly responsible for the large observed luminosity mismatch between them.
However, when intrinsic luminosities are derived by correcting for beaming
effects, this mismatch is significantly reduced. We show that spin plays an
important role to reveal the dichotomy of luminosity distributions between BL
Lacs and FSRQs, suggesting BL Lacs to be low luminous and slow rotators
compared to FSRQs.
Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows. (arXiv:1302.3067v1 [astro-ph.HE])
Nucleosynthesis in the gamma-ray burst accretion disks and associated outflows. (arXiv:1302.3067v1 [astro-ph.HE]):
We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion
disks formed by the Type II collapsars and outflows launched from these disks.
We deal with accretion disks having relatively low accretion rates: 0.001 M_sun
s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection
dominated. We report the synthesis of several unusual nuclei like 31P, 39K,
43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and
copper in the disk. We also confirm that isotopes of iron, cobalt, nickel,
argon, calcium, sulphur and silicon get synthesized in the disk, as shown by
previous authors. Much of these heavy elements thus synthesized are ejected
from the disk and survive in the outflows. Indeed, emission lines of many of
these heavy elements have been observed in the X-ray afterglows of several
GRBs.
We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion
disks formed by the Type II collapsars and outflows launched from these disks.
We deal with accretion disks having relatively low accretion rates: 0.001 M_sun
s^{-1} <~ Mdot <~ 0.01 M_sun s^{-1} and hence they are predominantly advection
dominated. We report the synthesis of several unusual nuclei like 31P, 39K,
43Sc, 35Cl and various isotopes of titanium, vanadium, chromium, manganese and
copper in the disk. We also confirm that isotopes of iron, cobalt, nickel,
argon, calcium, sulphur and silicon get synthesized in the disk, as shown by
previous authors. Much of these heavy elements thus synthesized are ejected
from the disk and survive in the outflows. Indeed, emission lines of many of
these heavy elements have been observed in the X-ray afterglows of several
GRBs.
A Monte Carlo Code for Relativistic Radiation Transport Around Kerr Black Holes. (arXiv:1302.3214v1 [astro-ph.HE])
A Monte Carlo Code for Relativistic Radiation Transport Around Kerr Black Holes. (arXiv:1302.3214v1 [astro-ph.HE]):
We present a new code for radiation transport around Kerr black holes,
including arbitrary emission and absorption terms, as well as electron
scattering and polarization. The code is particularly useful for analyzing
accretion flows made up of optically thick disks and optically thin coronae. We
give a detailed description of the methods employed in the code, and also
present results from a number of numerical tests to assess its accuracy and
convergence.
We present a new code for radiation transport around Kerr black holes,
including arbitrary emission and absorption terms, as well as electron
scattering and polarization. The code is particularly useful for analyzing
accretion flows made up of optically thick disks and optically thin coronae. We
give a detailed description of the methods employed in the code, and also
present results from a number of numerical tests to assess its accuracy and
convergence.
On the Star Formation-AGN Connection at $z \lesssim 0.3$. (arXiv:1302.2631v1 [astro-ph.CO])
On the Star Formation-AGN Connection at $z \lesssim 0.3$. (arXiv:1302.2631v1 [astro-ph.CO]):
Using the spectra of a sample of $\sim$28,000 nearby obscured active galaxies
from Data Release 7 of the Sloan Digital Sky Survey (SDSS), we probe the
connection between AGN activity and star formation over a range of radial
scales in the host galaxy. We use the extinction-corrected luminosity of the
[OIII] 5007 \AA\ line as a proxy of intrinsic AGN power and supermassive black
hole (SMBH) accretion rate. The star formation rates (SFRs) are taken from the
MPA-JHU value-added catalog and are measured through the 3$^{\prime\prime}$
SDSS aperture. We construct matched samples of galaxies covering a range in
redshifts. With increasing redshift, the projected aperture size encompasses
increasing amounts of the host galaxy. This allows us to trace the radial
distribution of star-formation as a function of AGN luminosity. We find that
the star formation becomes more centrally concentrated with increasing AGN
luminosity and Eddington ratio. This implies that such circumnuclear star
formation is associated with AGN activity, and that it increasingly dominates
over omnipresent disk star formation at higher AGN luminosities, placing
critical constraints on theoretical models that link host galaxy star formation
and SMBH fueling. We parametrize this relationship and find that the star
formation on radial scales ${body}lt;$1.7 kpc, when including a constant disk
component, has a sub-linear dependence on SMBH accretion rate: $SFR \propto
\dot{M}^{0.36}$, suggesting that angular momentum transfer through the disk
limits accretion efficiency rather than the supply from stellar mass loss.
Using the spectra of a sample of $\sim$28,000 nearby obscured active galaxies
from Data Release 7 of the Sloan Digital Sky Survey (SDSS), we probe the
connection between AGN activity and star formation over a range of radial
scales in the host galaxy. We use the extinction-corrected luminosity of the
[OIII] 5007 \AA\ line as a proxy of intrinsic AGN power and supermassive black
hole (SMBH) accretion rate. The star formation rates (SFRs) are taken from the
MPA-JHU value-added catalog and are measured through the 3$^{\prime\prime}$
SDSS aperture. We construct matched samples of galaxies covering a range in
redshifts. With increasing redshift, the projected aperture size encompasses
increasing amounts of the host galaxy. This allows us to trace the radial
distribution of star-formation as a function of AGN luminosity. We find that
the star formation becomes more centrally concentrated with increasing AGN
luminosity and Eddington ratio. This implies that such circumnuclear star
formation is associated with AGN activity, and that it increasingly dominates
over omnipresent disk star formation at higher AGN luminosities, placing
critical constraints on theoretical models that link host galaxy star formation
and SMBH fueling. We parametrize this relationship and find that the star
formation on radial scales ${body}lt;$1.7 kpc, when including a constant disk
component, has a sub-linear dependence on SMBH accretion rate: $SFR \propto
\dot{M}^{0.36}$, suggesting that angular momentum transfer through the disk
limits accretion efficiency rather than the supply from stellar mass loss.
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO])
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO]):
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
X-ray diagnostics of chemical composition of the accretion disk and donor star in ultra-compact X-ray binaries. (arXiv:1302.2070v1 [astro-ph.HE])
X-ray diagnostics of chemical composition of the accretion disk and donor star in ultra-compact X-ray binaries. (arXiv:1302.2070v1 [astro-ph.HE]):
Non-solar composition of the donor star in ultra-compact X-ray binaries may
have a pronounced effect on the fluorescent lines appearing in their spectra
due to reprocessing of primary radiation by the accretion disk and the white
dwarf surface. We show that the most dramatic and easily observable consequence
of the anomalous C/O abundance, is the significant, by more than an order of
magnitude, attenuation of the Ka line of iron. It is caused by screening of the
presence of iron by oxygen - in the C/O dominated material the main interaction
process for a E ~ 7keV photon is absorption by oxygen rather than by iron,
contrary to the solar composition case. Ionization of oxygen at high mass
accretion rates adds a luminosity dependence to this behavior - the iron line
is significantly suppressed only at low luminosity, log(LX) less than 37-37.5,
and should recover its nominal strength at higher luminosity. The increase of
the EW of the Ka lines of carbon and oxygen, on the other hand, saturates at
rather moderate values. Screening by He is less important, due to its low
ionization threshold and because in the accretion disk it is mostly ionized.
Consequently, in the case of the He-rich donor, the iron line strength remains
close to its nominal value, determined by the iron abundance in the accretion
disk. This opens the possibility of constraining the nature of donor stars in
UCXBs by means of X-ray spectroscopy with moderate energy resolution.
Non-solar composition of the donor star in ultra-compact X-ray binaries may
have a pronounced effect on the fluorescent lines appearing in their spectra
due to reprocessing of primary radiation by the accretion disk and the white
dwarf surface. We show that the most dramatic and easily observable consequence
of the anomalous C/O abundance, is the significant, by more than an order of
magnitude, attenuation of the Ka line of iron. It is caused by screening of the
presence of iron by oxygen - in the C/O dominated material the main interaction
process for a E ~ 7keV photon is absorption by oxygen rather than by iron,
contrary to the solar composition case. Ionization of oxygen at high mass
accretion rates adds a luminosity dependence to this behavior - the iron line
is significantly suppressed only at low luminosity, log(LX) less than 37-37.5,
and should recover its nominal strength at higher luminosity. The increase of
the EW of the Ka lines of carbon and oxygen, on the other hand, saturates at
rather moderate values. Screening by He is less important, due to its low
ionization threshold and because in the accretion disk it is mostly ionized.
Consequently, in the case of the He-rich donor, the iron line strength remains
close to its nominal value, determined by the iron abundance in the accretion
disk. This opens the possibility of constraining the nature of donor stars in
UCXBs by means of X-ray spectroscopy with moderate energy resolution.
Upper bounds on r-mode amplitudes from observations of LMXB neutron stars. (arXiv:1302.1204v1 [astro-ph.HE])
Upper bounds on r-mode amplitudes from observations of LMXB neutron stars. (arXiv:1302.1204v1 [astro-ph.HE]):
The r-mode oscillations of neutron stars can be potentially powerful probes
of cold ultra-dense matter. In this paper we present upper limits on the
amplitude of r-mode oscillations, and their gravitational-radiation-induced
spin-down rates, in low mass X-ray binary (LMXB) neutron stars under the
assumption that the quiescent neutron star luminosity is powered by dissipation
from a steady-state r-mode. We compute results for neutron star models
constructed with the APR equation of state for masses of 1.4, 2 and 2.21
M_{sun}. For the lower mass models (1.4 and 2 M_{sun}) we find dimensionless
r-mode amplitudes in the range from about 1x10^{-8} to 1.5x10^{-6}. For the
accreting millisecond X-ray pulsar (AMXP) sources with known quiescent
spin-down rates these limits suggest that about 1% of the observed rate can be
due to an unstable r-mode. Interestingly, the AMXP with the highest amplitude
limit, NGC 6640, could have an r-mode spin-down rate comparable to the
observed, quiescent rate for SAX J1808-3658. Thus, quiescent spin-down
measurements for this source would be particularly interesting. For all the
sources considered here our amplitude limits suggest that their gravitational
wave signals are likely too weak for detection with Advanced LIGO. Our highest
mass model (2.21 M_{sun}) can support enhanced, direct Urca neutrino emission
in the core and thus can have higher r-mode amplitudes. Indeed, the inferred
r-mode spin-down rates at these higher amplitudes are inconsistent with the
observed spin-down rates for some of the sources, such as IGR J00291+5934 and
XTE J1751-305. This can be used to place an upper limit on the masses of these
sources if they are made of normal nuclear matter, or alternatively it could be
used to probe the existence of exotic matter in them if their masses were
known.
The r-mode oscillations of neutron stars can be potentially powerful probes
of cold ultra-dense matter. In this paper we present upper limits on the
amplitude of r-mode oscillations, and their gravitational-radiation-induced
spin-down rates, in low mass X-ray binary (LMXB) neutron stars under the
assumption that the quiescent neutron star luminosity is powered by dissipation
from a steady-state r-mode. We compute results for neutron star models
constructed with the APR equation of state for masses of 1.4, 2 and 2.21
M_{sun}. For the lower mass models (1.4 and 2 M_{sun}) we find dimensionless
r-mode amplitudes in the range from about 1x10^{-8} to 1.5x10^{-6}. For the
accreting millisecond X-ray pulsar (AMXP) sources with known quiescent
spin-down rates these limits suggest that about 1% of the observed rate can be
due to an unstable r-mode. Interestingly, the AMXP with the highest amplitude
limit, NGC 6640, could have an r-mode spin-down rate comparable to the
observed, quiescent rate for SAX J1808-3658. Thus, quiescent spin-down
measurements for this source would be particularly interesting. For all the
sources considered here our amplitude limits suggest that their gravitational
wave signals are likely too weak for detection with Advanced LIGO. Our highest
mass model (2.21 M_{sun}) can support enhanced, direct Urca neutrino emission
in the core and thus can have higher r-mode amplitudes. Indeed, the inferred
r-mode spin-down rates at these higher amplitudes are inconsistent with the
observed spin-down rates for some of the sources, such as IGR J00291+5934 and
XTE J1751-305. This can be used to place an upper limit on the masses of these
sources if they are made of normal nuclear matter, or alternatively it could be
used to probe the existence of exotic matter in them if their masses were
known.
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO])
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO]):
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO])
Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3. (arXiv:1302.0113v1 [astro-ph.CO]):
In order to understand the mutual influence between active galactic nuclei
(AGN) and star formation during the evolution of galaxies, we investigate 142
galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic
Evolution Survey) field. All of our data are obtained from archive, X-ray point
source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m
point source catalog from Spitzer-MIPS observation. Although the IRAC colors of
our samples indicate the existence of star formation, the ratio of rest frame
2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN
predominates the spectral energy distribution (SED). We identify obscured AGN
in these 70{\mu}m luminous galaxies as characterized by a larger hardness
ratio. The higher X-ray obscuration fraction indicates an extra contribution
from the star formation in the host galaxy in addition to the usual AGN dusty
torus. If AGN feedback occurs in their host galaxies, the star formation must
be quenched and dust in host galaxy will be dispersed. However, our temperature
fitting shows there is no significant dust temperature enhancement in
far-infrared wavelength, suggesting the thermal radiative feedback is absent
from the AGN to the galaxy.
In order to understand the mutual influence between active galactic nuclei
(AGN) and star formation during the evolution of galaxies, we investigate 142
galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic
Evolution Survey) field. All of our data are obtained from archive, X-ray point
source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m
point source catalog from Spitzer-MIPS observation. Although the IRAC colors of
our samples indicate the existence of star formation, the ratio of rest frame
2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN
predominates the spectral energy distribution (SED). We identify obscured AGN
in these 70{\mu}m luminous galaxies as characterized by a larger hardness
ratio. The higher X-ray obscuration fraction indicates an extra contribution
from the star formation in the host galaxy in addition to the usual AGN dusty
torus. If AGN feedback occurs in their host galaxies, the star formation must
be quenched and dust in host galaxy will be dispersed. However, our temperature
fitting shows there is no significant dust temperature enhancement in
far-infrared wavelength, suggesting the thermal radiative feedback is absent
from the AGN to the galaxy.
Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron spectrum at young supernova remnants. (arXiv:1301.7499v1 [astro-ph.HE])
Synchrotron X-ray diagnostics of cutoff shape of nonthermal electron spectrum at young supernova remnants. (arXiv:1301.7499v1 [astro-ph.HE]):
Context: The synchrotron X-rays can be a useful tool to investigate the
electron acceleration at young supernova remnants (SNRs). Aims: At present,
since the magnetic field configuration around the shocks of SNRs is uncertain,
it is not clear whether the electron acceleration is limited by SNR age,
synchrotron cooling, or even escape from the acceleration region. We study if
the acceleration mechanism can be constrained by the cutoff shape of the
electron spectrum around the maximum energy. Methods: We derive analytical
formulae of the cutoff shape in each case where the maximum electron energy is
determined by SNR age, synchrotron cooling and escape from the shock. They are
related to the energy dependence of the electron diffusion coefficient. Next,
we discuss whether information on the cutoff shape is provided by near future
observations which gives simply the photon indices and the flux ratios in the
soft and hard X-ray bands. Results: If the power-law index of the electron
spectrum is independently determined by other observations, then we can
constrain the cutoff shape by comparing theoretical predictions of the photon
indices and/or the flux ratios with observed data which will be measured by
NuStar and/or Astro-H. Such study is helpful in understanding the acceleration
mechanism. In particular, it will bring us another independent constraint on
the magnetic field strength around the shocks of SNRs.
Context: The synchrotron X-rays can be a useful tool to investigate the
electron acceleration at young supernova remnants (SNRs). Aims: At present,
since the magnetic field configuration around the shocks of SNRs is uncertain,
it is not clear whether the electron acceleration is limited by SNR age,
synchrotron cooling, or even escape from the acceleration region. We study if
the acceleration mechanism can be constrained by the cutoff shape of the
electron spectrum around the maximum energy. Methods: We derive analytical
formulae of the cutoff shape in each case where the maximum electron energy is
determined by SNR age, synchrotron cooling and escape from the shock. They are
related to the energy dependence of the electron diffusion coefficient. Next,
we discuss whether information on the cutoff shape is provided by near future
observations which gives simply the photon indices and the flux ratios in the
soft and hard X-ray bands. Results: If the power-law index of the electron
spectrum is independently determined by other observations, then we can
constrain the cutoff shape by comparing theoretical predictions of the photon
indices and/or the flux ratios with observed data which will be measured by
NuStar and/or Astro-H. Such study is helpful in understanding the acceleration
mechanism. In particular, it will bring us another independent constraint on
the magnetic field strength around the shocks of SNRs.
X-ray C-M relation: theory and observation. (arXiv:1301.7476v1 [astro-ph.CO])
X-ray C-M relation: theory and observation. (arXiv:1301.7476v1 [astro-ph.CO]):
[Abridged] Since fifteen years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
this relation has been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
By analyzing a total of 52 objects, simulated each time with different
physical recipes for the baryonic component, as well as 60 synthetic X-ray
images, we aim at determining if these discrepancies are real or artificial. In
particular, we investigate how the simulated concentration-mass relation
depends i) on the radial range used to derive the concentration, ii) on the
presence of baryons in the simulations, and on the prescription used to
reproduce the gas. Finally, we evaluate iii) how the results differ when
adopting an X-ray approach for the analysis and iv) how the selection functions
based on X-ray luminosity, temperature, and SZ-signal can impact the results.
All effects studied go in the direction of explaining the discrepancy between
observations and simulations, but they contribute at different levels: while
the fitting radial range and the baryonic component play only a minor role, the
X-ray approach and selection function have profound repercussion on the
results.
RKS Note: Important paper comparing simulated clusters with observed ones, especially in regard to extracting cosmological parameters.
[Abridged] Since fifteen years, the concentration-mass relation has been
investigated diffusely in theoretical studies. On the other hand, only recently
this relation has been derived from X-ray observations. When that happened, the
results caused a certain level of concern: the X-ray normalizations and slopes
were found significantly dissimilar from those predicted by theory.
By analyzing a total of 52 objects, simulated each time with different
physical recipes for the baryonic component, as well as 60 synthetic X-ray
images, we aim at determining if these discrepancies are real or artificial. In
particular, we investigate how the simulated concentration-mass relation
depends i) on the radial range used to derive the concentration, ii) on the
presence of baryons in the simulations, and on the prescription used to
reproduce the gas. Finally, we evaluate iii) how the results differ when
adopting an X-ray approach for the analysis and iv) how the selection functions
based on X-ray luminosity, temperature, and SZ-signal can impact the results.
All effects studied go in the direction of explaining the discrepancy between
observations and simulations, but they contribute at different levels: while
the fitting radial range and the baryonic component play only a minor role, the
X-ray approach and selection function have profound repercussion on the
results.
RKS Note: Important paper comparing simulated clusters with observed ones, especially in regard to extracting cosmological parameters.
Investigating the Potential Dilution of the Metal Content of Hot Gas in Early-Type Galaxies by Accreted Cold Gas. (arXiv:1301.7706v1 [astro-ph.CO])
Investigating the Potential Dilution of the Metal Content of Hot Gas in Early-Type Galaxies by Accreted Cold Gas. (arXiv:1301.7706v1 [astro-ph.CO]):
The measured emission-weighted metal abundance of the hot gas in early-type
galaxies has been known to be lower than theoretical expectations for 20 years.
In addition, both X-ray luminosity and metal abundance vary significantly among
galaxies of similar optical luminosities. This suggests some missing factors in
the galaxy evolution process, especially the metal enrichment process. With
{\it Chandra} and {\it XMM-Newton}, we studied 32 early-type galaxies (kT
$\lesssim$ 1 keV) covering a span of two orders of $L_{X,\rm gas}/L_{K}$ to
investigate these missing factors. Contrary to previous studies that X-ray
faint galaxies show extremely low Fe abundance ($\sim 0.1$ Z${_\odot}$), nearly
all galaxies in our sample show an Fe abundance at least 0.3 Z${_\odot}$,
although the measured Fe abundance difference between X-ray faint and X-ray
bright galaxies remains remarkable. We investigated whether this dichotomy of
hot gas Fe abundances can be related to the dilution of hot gas by mixing with
cold gas. With a subset of 24 galaxies in this sample, we find that there is
virtually no correlation between hot gas Fe abundances and their atomic gas
content, which disproves the scenario that the low metal abundance of X-ray
faint galaxies might be a result of the dilution of the remaining hot gas by
pristine atomic gas. In contrast, we demonstrate a negative correlation between
the measured hot gas Fe abundance and the ratio of molecular gas mass to hot
gas mass, although it is unclear what is responsible for this apparent
anti-correlation. We discuss several possibilities including that externally
originated molecular gas might be able to dilute the hot gas metal content.
The measured emission-weighted metal abundance of the hot gas in early-type
galaxies has been known to be lower than theoretical expectations for 20 years.
In addition, both X-ray luminosity and metal abundance vary significantly among
galaxies of similar optical luminosities. This suggests some missing factors in
the galaxy evolution process, especially the metal enrichment process. With
{\it Chandra} and {\it XMM-Newton}, we studied 32 early-type galaxies (kT
$\lesssim$ 1 keV) covering a span of two orders of $L_{X,\rm gas}/L_{K}$ to
investigate these missing factors. Contrary to previous studies that X-ray
faint galaxies show extremely low Fe abundance ($\sim 0.1$ Z${_\odot}$), nearly
all galaxies in our sample show an Fe abundance at least 0.3 Z${_\odot}$,
although the measured Fe abundance difference between X-ray faint and X-ray
bright galaxies remains remarkable. We investigated whether this dichotomy of
hot gas Fe abundances can be related to the dilution of hot gas by mixing with
cold gas. With a subset of 24 galaxies in this sample, we find that there is
virtually no correlation between hot gas Fe abundances and their atomic gas
content, which disproves the scenario that the low metal abundance of X-ray
faint galaxies might be a result of the dilution of the remaining hot gas by
pristine atomic gas. In contrast, we demonstrate a negative correlation between
the measured hot gas Fe abundance and the ratio of molecular gas mass to hot
gas mass, although it is unclear what is responsible for this apparent
anti-correlation. We discuss several possibilities including that externally
originated molecular gas might be able to dilute the hot gas metal content.
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity. (arXiv:1301.7748v1 [astro-ph.SR])
A coordinated optical and X-ray spectroscopic campaign on HD179949: searching for planet-induced chromospheric and coronal activity. (arXiv:1301.7748v1 [astro-ph.SR]):
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle.
HD179949 is an F8V star, orbited by a close-in giant planet with a period of
~3 days. Previous studies suggested that the planet enhances the magnetic
activity of the parent star, producing a chromospheric hot spot which rotates
in phase with the planet orbit. However, this phenomenon is intermittent since
it was observed in several but not all seasons. A long-term monitoring of the
magnetic activity of HD179949 is required to study the amplitude and time
scales of star-planet interactions. In 2009 we performed a simultaneous optical
and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949
during ~5 orbital periods and ~2 stellar rotations. We analyzed the CaII H&K
lines as a proxy for chromospheric activity, and we studied the X-ray emission
in search of flux modulations and to determine basic properties of the coronal
plasma. A detailed analysis of the flux in the cores of the CaII H&K lines and
a similar study of the X-ray photometry shows evidence of source variability,
including one flare. The analysis of the the time series of chromospheric data
indicates a modulation with a ~11 days period, compatible with the stellar
rotation period at high latitudes. Instead, the X-ray light curve suggests a
signal with a period of ~4 days, consistent with the presence of two active
regions on opposite hemispheres. The observed variability can be explained,
most likely, as due to rotational modulation and to intrinsic evolution of
chromospheric and coronal activity. There is no clear signature related to the
orbital motion of the planet, but the possibility that just a fraction of the
chromospheric and coronal variability is modulated with the orbital period of
the planet, or the stellar-planet beat period, cannot be excluded. We conclude
that any effect due to the presence of the planet is difficult to disentangle.
Observational constraints on the powering mechanism of transient relativistic jets. (arXiv:1301.6771v1 [astro-ph.HE])
Observational constraints on the powering mechanism of transient relativistic jets. (arXiv:1301.6771v1 [astro-ph.HE]):
We revisit the paradigm of the dependency of jet power on black hole spin in
accreting black hole systems. In a previous paper we showed that the luminosity
of compact jets continuously launched due to accretion onto black holes in
X-ray binaries (analogous to those that dominate the kinetic feedback from AGN)
do not appear to correlate with reported black hole spin measurements. It is
therefore unclear whether extraction of the black hole spin energy is the main
driver powering compact jets from accreting black holes. Occasionally, black
hole X-ray binaries produce discrete, transient (ballistic) jets for a brief
time over accretion state changes. Here, we quantify the dependence of the
power of these transient jets (adopting two methods to infer the jet power) on
black hole spin, making use of all the available data in the current
literature, which includes 12 BHs with both measured spin parameters and radio
flares over the state transition. In several sources, regular, well-sampled
radio monitoring has shown that the peak radio flux differs dramatically
depending on the outburst (up to a factor of 1000) whereas the total power
required to energise the flare may only differ by a factor ~< 4 between
outbursts. The peak flux is determined by the total energy in the flare and the
time over which it is radiated (which can vary considerably between outbursts).
Using a Bayesian fitting routine we rule out a statistically significant
positive correlation between transient jet power measured using these methods,
and current estimates of black hole spin. Even when selecting subsamples of the
data that disregard some methods of black hole spin measurement or jet power
measurement, no correlation is found in all cases.
We revisit the paradigm of the dependency of jet power on black hole spin in
accreting black hole systems. In a previous paper we showed that the luminosity
of compact jets continuously launched due to accretion onto black holes in
X-ray binaries (analogous to those that dominate the kinetic feedback from AGN)
do not appear to correlate with reported black hole spin measurements. It is
therefore unclear whether extraction of the black hole spin energy is the main
driver powering compact jets from accreting black holes. Occasionally, black
hole X-ray binaries produce discrete, transient (ballistic) jets for a brief
time over accretion state changes. Here, we quantify the dependence of the
power of these transient jets (adopting two methods to infer the jet power) on
black hole spin, making use of all the available data in the current
literature, which includes 12 BHs with both measured spin parameters and radio
flares over the state transition. In several sources, regular, well-sampled
radio monitoring has shown that the peak radio flux differs dramatically
depending on the outburst (up to a factor of 1000) whereas the total power
required to energise the flare may only differ by a factor ~< 4 between
outbursts. The peak flux is determined by the total energy in the flare and the
time over which it is radiated (which can vary considerably between outbursts).
Using a Bayesian fitting routine we rule out a statistically significant
positive correlation between transient jet power measured using these methods,
and current estimates of black hole spin. Even when selecting subsamples of the
data that disregard some methods of black hole spin measurement or jet power
measurement, no correlation is found in all cases.
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
A Two-Phase Low-velocity Outflow in the Seyfert 1 Galaxy Ark~564. (arXiv:1301.6138v1 [astro-ph.HE])
A Two-Phase Low-velocity Outflow in the Seyfert 1 Galaxy Ark~564. (arXiv:1301.6138v1 [astro-ph.HE]):
The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy
transmission gratings for 250 ks. We present the high resolution X-ray spectrum
that shows several associated absorption lines. The photoionization model
requires two warm absorbers with two different ionization states
(logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities
(~100 km s^-1) and relatively low line of sight column densities (logNH=20.94
and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII,
OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase
produces lines at lower energies (OVI & OVII). The pressure--temperature
equilibrium curve for the Ark 564 absorber does not have the typical "S" shape,
even if the metallicity is super-solar; as a result the two warm-absorber
phases do not appear to be in pressure balance. This suggests that the
continuum incident on the absorbing gas is perhaps different from the observed
continuum. We also estimated the mass outflow rate and the associated kinetic
energy and find it to be at most 0.006% of the bolometric luminosity of
Ark~564. Thus it is highly unlikely that these outflows provide significant
feedback required by the galaxy formation models.
The Seyfert 1 galaxy Ark 564 was observed with Chandra high energy
transmission gratings for 250 ks. We present the high resolution X-ray spectrum
that shows several associated absorption lines. The photoionization model
requires two warm absorbers with two different ionization states
(logU=0.39\pm0.03 and logU=-0.99\pm0.13), both with moderate outflow velocities
(~100 km s^-1) and relatively low line of sight column densities (logNH=20.94
and 20.11 cm^-2). The high ionization phase produces absorption lines of OVII,
OVIII, NeIX, NeX, MgXI, FeXVII and FeXVIII while the low ionization phase
produces lines at lower energies (OVI & OVII). The pressure--temperature
equilibrium curve for the Ark 564 absorber does not have the typical "S" shape,
even if the metallicity is super-solar; as a result the two warm-absorber
phases do not appear to be in pressure balance. This suggests that the
continuum incident on the absorbing gas is perhaps different from the observed
continuum. We also estimated the mass outflow rate and the associated kinetic
energy and find it to be at most 0.006% of the bolometric luminosity of
Ark~564. Thus it is highly unlikely that these outflows provide significant
feedback required by the galaxy formation models.
Discovery of Relativistic Outflow in the Seyfert Galaxy Ark 564. (arXiv:1301.6139v1 [astro-ph.HE])
Discovery of Relativistic Outflow in the Seyfert Galaxy Ark 564. (arXiv:1301.6139v1 [astro-ph.HE]):
We present Chandra high energy transmission grating spectra of the
narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption
lines which are well modeled with low velocity outflow components usually
observed in Seyfert galaxies (Gupta et al. 2013). There are, however, some
residual absorption lines which are not accounted for by low-velocity outflows.
Here we present identifications of the strongest lines as K{\alpha} transitions
of OVII(two lines) and OVI at outflow velocities of ~0.1c. These lines are
detected at 6.9{\sigma}, 6.2{\sigma}, and 4.7{\sigma} respectively and cannot
be due to chance statistical fluctuations. Photoionization models with
ultra-high velocity components improves the spectral fit significantly,
providing further support for the presence of relativistic outflow in this
source. Without knowing the location of the absorber, its mass and energy
outflow rates cannot be well constrained; we find E$\dot{E}(outflow)/L_{bo}$
ranging from < 0.001% to 60% using different assumptions. This is the first
time that absorption lines with ultra-high velocities are unambiguously
detected in the soft X-ray band. The presence of outflows with relativistic
velocities in AGNs with Seyfert-type luminosities is hard to understand and
provides valuable constraints to models of AGN outflows.
We present Chandra high energy transmission grating spectra of the
narrow-line Seyfert-1 galaxy Ark 564. The spectrum shows numerous absorption
lines which are well modeled with low velocity outflow components usually
observed in Seyfert galaxies (Gupta et al. 2013). There are, however, some
residual absorption lines which are not accounted for by low-velocity outflows.
Here we present identifications of the strongest lines as K{\alpha} transitions
of OVII(two lines) and OVI at outflow velocities of ~0.1c. These lines are
detected at 6.9{\sigma}, 6.2{\sigma}, and 4.7{\sigma} respectively and cannot
be due to chance statistical fluctuations. Photoionization models with
ultra-high velocity components improves the spectral fit significantly,
providing further support for the presence of relativistic outflow in this
source. Without knowing the location of the absorber, its mass and energy
outflow rates cannot be well constrained; we find E$\dot{E}(outflow)/L_{bo}$
ranging from < 0.001% to 60% using different assumptions. This is the first
time that absorption lines with ultra-high velocities are unambiguously
detected in the soft X-ray band. The presence of outflows with relativistic
velocities in AGNs with Seyfert-type luminosities is hard to understand and
provides valuable constraints to models of AGN outflows.
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO])
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO]):
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
White Paper on GEMS Study of Polarized X-rays from Neutron Stars. (arXiv:1301.5514v2 [astro-ph.HE] UPDATED)
White Paper on GEMS Study of Polarized X-rays from Neutron Stars. (arXiv:1301.5514v2 [astro-ph.HE] UPDATED):
We examine the expected X-ray polarization properties of neutron-star X-ray
sources of various types, e.g., accretion and rotation powered pulsars,
magnetars, and low-mass X-ray binaries. We summarize the model calculations
leading to these expected properties. We describe how a comparison of these
with their observed properties, as inferred from GEMS data, will probe the
essential dynamical, electromagnetic, plasma, and emission processes in
neutron-star binaries, discriminate between models of these processes, and
constrain model parameters. An exciting goal is the first observational
demonstration in this context of the existence of vacuum resonance, a
fundamental quantum electrodynamical phenomenon first described in the 1930s.
We examine the expected X-ray polarization properties of neutron-star X-ray
sources of various types, e.g., accretion and rotation powered pulsars,
magnetars, and low-mass X-ray binaries. We summarize the model calculations
leading to these expected properties. We describe how a comparison of these
with their observed properties, as inferred from GEMS data, will probe the
essential dynamical, electromagnetic, plasma, and emission processes in
neutron-star binaries, discriminate between models of these processes, and
constrain model parameters. An exciting goal is the first observational
demonstration in this context of the existence of vacuum resonance, a
fundamental quantum electrodynamical phenomenon first described in the 1930s.
First results from a next-generation off-plane X-ray diffraction grating. (arXiv:1301.5531v1 [astro-ph.IM])
First results from a next-generation off-plane X-ray diffraction grating. (arXiv:1301.5531v1 [astro-ph.IM]):
Future NASA X-ray spectroscopy missions will require high throughput, high
resolution grating spectrometers. Off-plane reflection gratings are capable of
meeting the performance requirements needed to realize the scientific goals of
these missions. We have identified a novel grating fabrication method that
utilizes common lithographic and microfabrication techniques to produce the
high fidelity groove profile necessary to achieve this performance. Application
of this process has produced an initial pre-master that exhibits a radial
(variable line spacing along the groove dimension), high density (>6000
grooves/mm), laminar profile. This pre-master has been tested for diffraction
efficiency at the BESSY II synchrotron light facility and diffracts up to 55%
of incident light into usable spectral orders. Furthermore, tests of spectral
resolving power show that these gratings are capable of obtaining resolutions
well above 1300 ($\lambda/\Delta\lambda$) with limitations due to the test
apparatus, not the gratings. Obtaining these results has provided confidence
that this fabrication process is capable of producing off-plane reflection
gratings for the next generation of X-ray observatories.
Future NASA X-ray spectroscopy missions will require high throughput, high
resolution grating spectrometers. Off-plane reflection gratings are capable of
meeting the performance requirements needed to realize the scientific goals of
these missions. We have identified a novel grating fabrication method that
utilizes common lithographic and microfabrication techniques to produce the
high fidelity groove profile necessary to achieve this performance. Application
of this process has produced an initial pre-master that exhibits a radial
(variable line spacing along the groove dimension), high density (>6000
grooves/mm), laminar profile. This pre-master has been tested for diffraction
efficiency at the BESSY II synchrotron light facility and diffracts up to 55%
of incident light into usable spectral orders. Furthermore, tests of spectral
resolving power show that these gratings are capable of obtaining resolutions
well above 1300 ($\lambda/\Delta\lambda$) with limitations due to the test
apparatus, not the gratings. Obtaining these results has provided confidence
that this fabrication process is capable of producing off-plane reflection
gratings for the next generation of X-ray observatories.
Measuring Black Hole Spin using X-ray Reflection Spectroscopy. (arXiv:1302.3260v1 [astro-ph.HE])
Measuring Black Hole Spin using X-ray Reflection Spectroscopy. (arXiv:1302.3260v1 [astro-ph.HE]):
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.
G2 can Illuminate the Black Hole Population near the Galactic Center. (arXiv:1302.3220v1 [astro-ph.GA])
G2 can Illuminate the Black Hole Population near the Galactic Center. (arXiv:1302.3220v1 [astro-ph.GA]):
Galactic nuclei are expected to be densely populated with stellar and
intermediate mass black holes. Exploring this population will have important
consequences for the observation prospects of gravitational waves as well as
understanding galactic evolution. The gas cloud G2 currently approaching Sgr A*
provides an unprecedented opportunity to probe the black hole and neutron star
population of the Galactic nucleus. We examine the possibility of a G2-black
hole encounter and its detectability with current X-ray satellites, such as
Chandra and NuSTAR. We find that multiple encounters are likely to occur close
to the pericenter, which may be detectable upon favorable circumstances. This
opportunity provides an additional, important science case for leading X-ray
observatories to closely follow G2 on its way to the nucleus.
Galactic nuclei are expected to be densely populated with stellar and
intermediate mass black holes. Exploring this population will have important
consequences for the observation prospects of gravitational waves as well as
understanding galactic evolution. The gas cloud G2 currently approaching Sgr A*
provides an unprecedented opportunity to probe the black hole and neutron star
population of the Galactic nucleus. We examine the possibility of a G2-black
hole encounter and its detectability with current X-ray satellites, such as
Chandra and NuSTAR. We find that multiple encounters are likely to occur close
to the pericenter, which may be detectable upon favorable circumstances. This
opportunity provides an additional, important science case for leading X-ray
observatories to closely follow G2 on its way to the nucleus.
Monday, February 11, 2013
The UV and X-ray activity of the M dwarfs within 10pc of the Sun. (arXiv:1302.1061v1 [astro-ph.SR])
The UV and X-ray activity of the M dwarfs within 10pc of the Sun. (arXiv:1302.1061v1 [astro-ph.SR]):
We systematically study the X-ray and ultraviolet emission of a subsample of
M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10pc
to obtain a nearly volume-limited sample (~90% completeness). Archival ROSAT,
XMM-Newton and GALEX data are combined with published spectroscopic studies of
Halpha emission and rotation to obtain a broad picture of stellar activity on M
dwarfs. We make use of synthetic model spectra to determine the relative
contributions of photospheric and chromospheric emission to the ultraviolet
flux. We also analyse the same diagnostics for a comparison sample of young M
dwarfs in the TWHya association (~10Myrs). We find that generally the emission
in the GALEX bands is dominated by the chromosphere but the photospheric
component is not negligible in early-M field dwarfs. The surface fluxes for the
Halpha, near-ultraviolet, far-ultraviolet and X-ray emission are connected via
a power law dependence. We present here for the first time such flux-flux
relations involving broad-band ultraviolet emission for M dwarfs. For given
spectral type the activity indices, defined as flux ratio between the activity
diagnostic and the bolometric flux of the star, display a spread of 2-3 dex
which is largest for M4 stars. The mean activity index for fast rotators,
likely representing the saturation level, decreases from X-rays over the FUV to
the NUV band and Halpha, i.e. the fractional radiation output increases with
atmospheric height. The comparison to the ultraviolet and X-ray properties of
TWHya members shows a drop of nearly three orders of magnitude for the
luminosity in these bands between ~10Myr and few Gyrs age. A few young field
dwarfs (< 1Gyr) in the 10pc sample bridge the gap indicating that the drop in
magnetic activity with age is a continuous process. The slope of the age decay
is steeper for the X-ray than for the UV luminosity.
We systematically study the X-ray and ultraviolet emission of a subsample of
M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10pc
to obtain a nearly volume-limited sample (~90% completeness). Archival ROSAT,
XMM-Newton and GALEX data are combined with published spectroscopic studies of
Halpha emission and rotation to obtain a broad picture of stellar activity on M
dwarfs. We make use of synthetic model spectra to determine the relative
contributions of photospheric and chromospheric emission to the ultraviolet
flux. We also analyse the same diagnostics for a comparison sample of young M
dwarfs in the TWHya association (~10Myrs). We find that generally the emission
in the GALEX bands is dominated by the chromosphere but the photospheric
component is not negligible in early-M field dwarfs. The surface fluxes for the
Halpha, near-ultraviolet, far-ultraviolet and X-ray emission are connected via
a power law dependence. We present here for the first time such flux-flux
relations involving broad-band ultraviolet emission for M dwarfs. For given
spectral type the activity indices, defined as flux ratio between the activity
diagnostic and the bolometric flux of the star, display a spread of 2-3 dex
which is largest for M4 stars. The mean activity index for fast rotators,
likely representing the saturation level, decreases from X-rays over the FUV to
the NUV band and Halpha, i.e. the fractional radiation output increases with
atmospheric height. The comparison to the ultraviolet and X-ray properties of
TWHya members shows a drop of nearly three orders of magnitude for the
luminosity in these bands between ~10Myr and few Gyrs age. A few young field
dwarfs (< 1Gyr) in the 10pc sample bridge the gap indicating that the drop in
magnetic activity with age is a continuous process. The slope of the age decay
is steeper for the X-ray than for the UV luminosity.
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
Terrestrial effects of possible astrophysical sources of an AD 774-775 increase in 14C production. (arXiv:1302.1501v2 [astro-ph.SR] UPDATED)
Terrestrial effects of possible astrophysical sources of an AD 774-775 increase in 14C production. (arXiv:1302.1501v2 [astro-ph.SR] UPDATED):
We examine possible sources of a substantial increase in tree ring 14C
measurements for the years AD 774-775. Contrary to claims regarding a coronal
mass ejection (CME), the required CME energy is not several orders of magnitude
greater than known solar events. We consider solar proton events (SPEs) with
three different fluences and two different spectra. The data may be explained
by an event with fluence about one order of magnitude beyond the October 1989
SPE. Two hard spectrum cases considered here result in moderate ozone
depletion, so no mass extinction is implied, though we do predict increases in
erythema and damage to plants from enhanced solar UV. We are able to rule out
an event with a very soft spectrum that causes severe ozone depletion and
subsequent biological impacts. Nitrate enhancements are consistent with their
apparent absence in ice core data. The modern technological implications of
such an event may be extreme, and considering recent confirmation of
superflares on solar-type stars, this issue merits attention.
We examine possible sources of a substantial increase in tree ring 14C
measurements for the years AD 774-775. Contrary to claims regarding a coronal
mass ejection (CME), the required CME energy is not several orders of magnitude
greater than known solar events. We consider solar proton events (SPEs) with
three different fluences and two different spectra. The data may be explained
by an event with fluence about one order of magnitude beyond the October 1989
SPE. Two hard spectrum cases considered here result in moderate ozone
depletion, so no mass extinction is implied, though we do predict increases in
erythema and damage to plants from enhanced solar UV. We are able to rule out
an event with a very soft spectrum that causes severe ozone depletion and
subsequent biological impacts. Nitrate enhancements are consistent with their
apparent absence in ice core data. The modern technological implications of
such an event may be extreme, and considering recent confirmation of
superflares on solar-type stars, this issue merits attention.
To differentiate neutron star models by X-ray polarimetry. (arXiv:1302.1328v1 [astro-ph.HE])
To differentiate neutron star models by X-ray polarimetry. (arXiv:1302.1328v1 [astro-ph.HE]):
The nature of pulsar is still unknown because of non-perturbative effects of
the fundamental strong interaction, and different models of pulsar inner
structures are then suggested, either conventional neutron stars or quark
stars. Additionally, a state of quark-cluster matter is conjectured for cold
matter at supranuclear density, as a result pulsars could thus be quark-cluster
stars. Besides understanding different manifestations, the most important issue
is to find an effective way to observationally differentiate those models.
X-ray polarimetry would play an important role here. In this letter, we focus
on the thermal X-ray polarization of quark/quark-cluster stars. While the
thermal X-ray linear polarization percentage is typically higher than ~10% in
normal neutron star models, the percentage of quark/quark-cluster stars is
almost zero. It could then be an effective method to identify
quark/quark-cluster stars by soft X-ray polarimetry. We are therefore expecting
to detect thermal X-ray polarization in the coming decades.
The nature of pulsar is still unknown because of non-perturbative effects of
the fundamental strong interaction, and different models of pulsar inner
structures are then suggested, either conventional neutron stars or quark
stars. Additionally, a state of quark-cluster matter is conjectured for cold
matter at supranuclear density, as a result pulsars could thus be quark-cluster
stars. Besides understanding different manifestations, the most important issue
is to find an effective way to observationally differentiate those models.
X-ray polarimetry would play an important role here. In this letter, we focus
on the thermal X-ray polarization of quark/quark-cluster stars. While the
thermal X-ray linear polarization percentage is typically higher than ~10% in
normal neutron star models, the percentage of quark/quark-cluster stars is
almost zero. It could then be an effective method to identify
quark/quark-cluster stars by soft X-ray polarimetry. We are therefore expecting
to detect thermal X-ray polarization in the coming decades.
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO])
Nuclear Activity is more prevalent in Star-Forming Galaxies. (arXiv:1302.1202v1 [astro-ph.CO]):
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
We explore the question of whether low and moderate luminosity Active
Galactic Nuclei (AGNs) are preferentially found in galaxies that are undergoing
a transition from active star formation to quiescence. This notion has been
suggested by studies of the UV-to-optical colors of AGN hosts, which find them
to be common among galaxies in the so-called "Green Valley", a region of galaxy
color space believed to be composed mostly of galaxies undergoing
star-formation quenching. Combining the deepest current X-ray and Herschel.
PACS far-infrared (FIR) observations of the two Chandra Deep Fields (CDFs) with
redshifts, stellar masses and rest-frame photometry derived from the extensive
and uniform multi-wavelength data in these fields, we compare the rest-frame
U-V color distributions and SFR distributions of AGNs and carefully constructed
samples of inactive control galaxies. The UV-to-optical colors of AGNs are
consistent with equally massive inactive galaxies at redshifts out to z~2, but
we show that such colors are poor tracers of star formation. While the FIR
distributions of both star-forming AGNs and star-forming inactive galaxies are
statistically similar, we show that AGNs are preferentially found in
star-forming host galaxies, or, in other words, AGNs are less likely to be
found in weakly star-forming or quenched galaxies. We postulate that, among
X-ray selected AGNs of low and moderate accretion luminosities, the supply of
cold gas primarily determines the accretion rate distribution of the nuclear
black holes.
Discovery of Fe K{\alpha} X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314. (arXiv:1302.1761v1 [astro-ph.HE])
Discovery of Fe K{\alpha} X-ray reverberation around the black holes in MCG-5-23-16 and NGC 7314. (arXiv:1302.1761v1 [astro-ph.HE]):
Several X-ray observations have recently revealed the presence of
reverberation time delays between spectral components in AGN. Most of the
observed lags are between the power-law Comptonization component, seen
directly, and the soft excess produced by reflection in the vicinity of the
black hole. NGC 4151 was the first object to show these lags in the iron K
band. Here, we report the discovery of reverberation lags in the Fe K band in
two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band,
where the Fe K line peaks, lags the bands at lower and higher energies with a
time delay of ~ 1 kilo-seconds. These lags are unlikely to be due to the narrow
Fe K line. They are fully consistent with reverberation of the
relativistically-broadened iron K line. The measured lags, their time-scale and
spectral modeling, indicate that most of the radiation is emitted at ~ 5 and 24
gravitational radii for MCG-5-23-16 and NGC 7314 respectively.
Several X-ray observations have recently revealed the presence of
reverberation time delays between spectral components in AGN. Most of the
observed lags are between the power-law Comptonization component, seen
directly, and the soft excess produced by reflection in the vicinity of the
black hole. NGC 4151 was the first object to show these lags in the iron K
band. Here, we report the discovery of reverberation lags in the Fe K band in
two other sources: MCG-5-23-16 and NGC 7314. In both objects, the 6-7 keV band,
where the Fe K line peaks, lags the bands at lower and higher energies with a
time delay of ~ 1 kilo-seconds. These lags are unlikely to be due to the narrow
Fe K line. They are fully consistent with reverberation of the
relativistically-broadened iron K line. The measured lags, their time-scale and
spectral modeling, indicate that most of the radiation is emitted at ~ 5 and 24
gravitational radii for MCG-5-23-16 and NGC 7314 respectively.
X-ray Irradiation of the LkCa 15 Protoplanetary Disk. (arXiv:1302.2111v1 [astro-ph.SR])
X-ray Irradiation of the LkCa 15 Protoplanetary Disk. (arXiv:1302.2111v1 [astro-ph.SR]):
LkCa 15 in the Taurus star-forming region has recently gained attention as
the first accreting T Tauri star likely to host a young protoplanet. High
spatial resolution infrared observations have detected the suspected
protoplanet within a dust-depleted inner gap of the LkCa 15 transition disk at
a distance of 15 AU from the star. If this object's status as a protoplanet is
confirmed, LkCa 15 will serve as a unique laboratory for constraining physical
conditions within a planet-forming disk. Previous models of the LkCa 15 disk
have accounted for disk heating by the stellar photosphere but have ignored the
potential importance of X-ray ionization and heating. We report here the
detection of LkCa 15 as a bright X-ray source with Chandra. The X-ray emission
is characterized by a cool heavily-absorbed plasma component at kT_cool ~0.3
keV and a harder component at kT_hot ~5 keV. We use the observed X-ray
properties to provide initial estimates of the X-ray ionization and heating
rates within the tenuous inner disk. These estimates and the observed X-ray
properties of LkCa 15 can be used as a starting point for developing more
realistic disk models of this benchmark system.
LkCa 15 in the Taurus star-forming region has recently gained attention as
the first accreting T Tauri star likely to host a young protoplanet. High
spatial resolution infrared observations have detected the suspected
protoplanet within a dust-depleted inner gap of the LkCa 15 transition disk at
a distance of 15 AU from the star. If this object's status as a protoplanet is
confirmed, LkCa 15 will serve as a unique laboratory for constraining physical
conditions within a planet-forming disk. Previous models of the LkCa 15 disk
have accounted for disk heating by the stellar photosphere but have ignored the
potential importance of X-ray ionization and heating. We report here the
detection of LkCa 15 as a bright X-ray source with Chandra. The X-ray emission
is characterized by a cool heavily-absorbed plasma component at kT_cool ~0.3
keV and a harder component at kT_hot ~5 keV. We use the observed X-ray
properties to provide initial estimates of the X-ray ionization and heating
rates within the tenuous inner disk. These estimates and the observed X-ray
properties of LkCa 15 can be used as a starting point for developing more
realistic disk models of this benchmark system.
The Evolution of Active Galactic Nuclei in Warm Dark Matter Cosmology. (arXiv:1302.2000v1 [astro-ph.CO])
The Evolution of Active Galactic Nuclei in Warm Dark Matter Cosmology. (arXiv:1302.2000v1 [astro-ph.CO]):
Recent measurements of the abundance of AGN with low-luminosities (L_X< 10^44
erg/s in the 2-10 keV energy band) at high redshifts z>4 provide a serious
challenge for Cold Dark Matter (CDM) models based on interaction-driven fueling
of AGN. Using a semi-analytic model of galaxy formation we investigate how such
observations fit in a Warm Dark Matter (WDM) scenario of galaxy formation, and
compare the results with those obtained in the standard CDM scenario with
different efficiencies for the stellar feedback. Taking on our previous
exploration of galaxy formation in WDM cosmology, we assume as a reference case
a spectrum which is suppressed - compared to the standard CDM case - below a
cut-off scale ~ 0.2$ Mpc corresponding (for thermal relic WDM particles) to a
mass m_X=0.75 keV. We run our fiducial semi-analytic model with such a WDM
spectrum to derive AGN luminosity functions from z~6 to the present over a wide
range of luminosities (10^43< L_X/erg/s < 10^46 in the 2-10 keV X-ray band), to
compare with recent observations and with the results in the CDM case. When
compared with the standard CDM case, the luminosity distributions we obtain
assuming a WDM spectrum are characterized by a similar behaviour at low
redshift, and by a flatter slope at faint magnitudes for z>3, which provide an
excellent fit to present observations. We discuss how such a result compares
with CDM models with maximized feedback efficiency, and how future deep AGN
surveys will allow for a better discrimination between feedback and
cosmological effects on the evolution of AGN in interaction-driven models for
AGN fueling.
Recent measurements of the abundance of AGN with low-luminosities (L_X< 10^44
erg/s in the 2-10 keV energy band) at high redshifts z>4 provide a serious
challenge for Cold Dark Matter (CDM) models based on interaction-driven fueling
of AGN. Using a semi-analytic model of galaxy formation we investigate how such
observations fit in a Warm Dark Matter (WDM) scenario of galaxy formation, and
compare the results with those obtained in the standard CDM scenario with
different efficiencies for the stellar feedback. Taking on our previous
exploration of galaxy formation in WDM cosmology, we assume as a reference case
a spectrum which is suppressed - compared to the standard CDM case - below a
cut-off scale ~ 0.2$ Mpc corresponding (for thermal relic WDM particles) to a
mass m_X=0.75 keV. We run our fiducial semi-analytic model with such a WDM
spectrum to derive AGN luminosity functions from z~6 to the present over a wide
range of luminosities (10^43< L_X/erg/s < 10^46 in the 2-10 keV X-ray band), to
compare with recent observations and with the results in the CDM case. When
compared with the standard CDM case, the luminosity distributions we obtain
assuming a WDM spectrum are characterized by a similar behaviour at low
redshift, and by a flatter slope at faint magnitudes for z>3, which provide an
excellent fit to present observations. We discuss how such a result compares
with CDM models with maximized feedback efficiency, and how future deep AGN
surveys will allow for a better discrimination between feedback and
cosmological effects on the evolution of AGN in interaction-driven models for
AGN fueling.
High density matter. (arXiv:1302.1928v1 [astro-ph.SR])
High density matter. (arXiv:1302.1928v1 [astro-ph.SR]):
The microscopic composition and properties of matter at super-saturation
densities have been the subject of intense investigation for decades. The
scarcity of experimental and observational data has lead to the necessary
reliance on theoretical models. However, there remains great uncertainty in
these models, which, of necessity, have to go beyond the over-simple assumption
that high density matter consists only of nucleons and leptons. Heavy strange
baryons, mesons and quark matter in different forms and phases have to be
included to fulfil basic requirements of fundamental laws of physics. In this
review the latest developments in construction of the Equation of State (EoS)
of high-density matter at zero and finite temperature assuming different
composition of the matter are surveyed. Critical comparison of model EoS with
available observational data on neutron stars, including gravitational masses,
radii and cooling patterns is presented. The effect of changing rotational
frequency on the composition of neutron stars during their lifetime is
demonstrated. Compatibility of EoS of high-density, low temperature compact
objects and low density, high temperature matter created in heavy-ion
collisions is discussed.
The microscopic composition and properties of matter at super-saturation
densities have been the subject of intense investigation for decades. The
scarcity of experimental and observational data has lead to the necessary
reliance on theoretical models. However, there remains great uncertainty in
these models, which, of necessity, have to go beyond the over-simple assumption
that high density matter consists only of nucleons and leptons. Heavy strange
baryons, mesons and quark matter in different forms and phases have to be
included to fulfil basic requirements of fundamental laws of physics. In this
review the latest developments in construction of the Equation of State (EoS)
of high-density matter at zero and finite temperature assuming different
composition of the matter are surveyed. Critical comparison of model EoS with
available observational data on neutron stars, including gravitational masses,
radii and cooling patterns is presented. The effect of changing rotational
frequency on the composition of neutron stars during their lifetime is
demonstrated. Compatibility of EoS of high-density, low temperature compact
objects and low density, high temperature matter created in heavy-ion
collisions is discussed.
Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster. (arXiv:1302.1917v1 [astro-ph.CO])
Dark Matter Subhalos and the X-ray Morphology of the Coma Cluster. (arXiv:1302.1917v1 [astro-ph.CO]):
Structure formation models predict that clusters of galaxies contain numerous
massive subhalos. The gravity of a subhalo in a cluster compresses the
surrounding intracluster gas and enhances its X-ray emission. We present a
simple model, which treats subhalos as slow moving and gasless, for computing
this effect. Recent weak lensing measurements by Okabe et al. (2010) have
determined masses of ~ 10^13 solar masses for three mass concentrations
projected within 300 kpc of the center of the Coma cluster, two of which are
centered on the giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a
smooth spheroidal beta-model for the gas distribution in the unperturbed
cluster, we model the effect of these subhalos on the X-ray morphology of the
Coma cluster, comparing our results to Chandra and XMM-Newton X-ray data. The
agreement between the models and the X-ray morphology of the central Coma
cluster is striking. With subhalo parameters from the lensing measurements, the
distances of the three subhalos from the Coma cluster midplane along our line
of sight are all tightly constrained. Using the model to fit the subhalo masses
for NGC 4889 and NGC 4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses,
respectively, in good agreement with the lensing masses. These results lend
strong support to the argument that NGC 4889 and NGC 4874 are each associated
with a subhalo that resides near the center of the Coma cluster. In addition to
constraining the masses and 3-d location of subhalos, the X-ray data show
promise as a means of probing the structure of central subhalos.
Structure formation models predict that clusters of galaxies contain numerous
massive subhalos. The gravity of a subhalo in a cluster compresses the
surrounding intracluster gas and enhances its X-ray emission. We present a
simple model, which treats subhalos as slow moving and gasless, for computing
this effect. Recent weak lensing measurements by Okabe et al. (2010) have
determined masses of ~ 10^13 solar masses for three mass concentrations
projected within 300 kpc of the center of the Coma cluster, two of which are
centered on the giant elliptical galaxies NGC 4889 and NGC 4874. Adopting a
smooth spheroidal beta-model for the gas distribution in the unperturbed
cluster, we model the effect of these subhalos on the X-ray morphology of the
Coma cluster, comparing our results to Chandra and XMM-Newton X-ray data. The
agreement between the models and the X-ray morphology of the central Coma
cluster is striking. With subhalo parameters from the lensing measurements, the
distances of the three subhalos from the Coma cluster midplane along our line
of sight are all tightly constrained. Using the model to fit the subhalo masses
for NGC 4889 and NGC 4874 gives 9.1 x 10^12 and 7.6 x 10^12 solar masses,
respectively, in good agreement with the lensing masses. These results lend
strong support to the argument that NGC 4889 and NGC 4874 are each associated
with a subhalo that resides near the center of the Coma cluster. In addition to
constraining the masses and 3-d location of subhalos, the X-ray data show
promise as a means of probing the structure of central subhalos.
Tuesday, February 5, 2013
Suzaku observations of Abell 1835 outskirts: Deviation from hydrostatic equilibrium. (arXiv:1302.0095v1 [astro-ph.CO])
Suzaku observations of Abell 1835 outskirts: Deviation from hydrostatic equilibrium. (arXiv:1302.0095v1 [astro-ph.CO]):
We present results of four-pointing Suzaku X-ray observations (total ~200 ks)
of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ~ 8 keV,
z = 0.253) out to the virial radius (r_vir ~ 2.9 Mpc) and beyond. Faint X-ray
emission from the ICM out to r_vir is detected. The temperature gradually
decreases with radius from ~8 keV in the inner region to ~2 keV at r_vir. The
entropy profile is shown to flatten beyond r_500, in disagreement with the
r_1.1 dependence predicted from the accretion shock heating model. The thermal
pressure profile in the range 0.3r_500 < r < r_vir agrees well with that
obtained from the stacked Sunyaev-Zel'dovich effect observations with the
Planck satellite. The hydrostatic mass profile in the cluster outskirts (r_500
< r < r_vir) falls well short of the weak lensing one derived from
Subaru/Suprime-Cam observations, showing an unphysical decrease with radius.
The gas mass fraction at r_vir defined with the lensing total mass agrees with
the cosmic baryon fraction from the WMAP 7-year data. All these results
indicate, rather than the gas-clumping effect, that the bulk of the ICM in the
cluster outskirts is far from hydrostatic equilibrium and infalling matter
retained some of its kinetic energy. Finally, combining with our recent Suzaku
and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and
redshift, we show that the cluster temperature distribution in the outskirts is
significantly correlated with the galaxy density field in the surrounding
large-scale environment at (1-2)r_vir.
We present results of four-pointing Suzaku X-ray observations (total ~200 ks)
of the intracluster medium (ICM) in the Abell 1835 galaxy cluster (kT ~ 8 keV,
z = 0.253) out to the virial radius (r_vir ~ 2.9 Mpc) and beyond. Faint X-ray
emission from the ICM out to r_vir is detected. The temperature gradually
decreases with radius from ~8 keV in the inner region to ~2 keV at r_vir. The
entropy profile is shown to flatten beyond r_500, in disagreement with the
r_1.1 dependence predicted from the accretion shock heating model. The thermal
pressure profile in the range 0.3r_500 < r < r_vir agrees well with that
obtained from the stacked Sunyaev-Zel'dovich effect observations with the
Planck satellite. The hydrostatic mass profile in the cluster outskirts (r_500
< r < r_vir) falls well short of the weak lensing one derived from
Subaru/Suprime-Cam observations, showing an unphysical decrease with radius.
The gas mass fraction at r_vir defined with the lensing total mass agrees with
the cosmic baryon fraction from the WMAP 7-year data. All these results
indicate, rather than the gas-clumping effect, that the bulk of the ICM in the
cluster outskirts is far from hydrostatic equilibrium and infalling matter
retained some of its kinetic energy. Finally, combining with our recent Suzaku
and lensing analysis of Abell 1689, a cluster of similar mass, temperature, and
redshift, we show that the cluster temperature distribution in the outskirts is
significantly correlated with the galaxy density field in the surrounding
large-scale environment at (1-2)r_vir.
XMM-Newton/RGS Detection of the Missing Interstellar OVII Kalpha Absorption Line in the Spectrum of Cyg X-2. (arXiv:1302.0076v1 [astro-ph.HE])
XMM-Newton/RGS Detection of the Missing Interstellar OVII Kalpha Absorption Line in the Spectrum of Cyg X-2. (arXiv:1302.0076v1 [astro-ph.HE]):
The hot interstellar medium is an important part of the Galactic ecosystem
and can be effectively characterized through X-ray absorption line
spectroscopy. However, in a study of the hot medium using the accreting neutron
star X-ray binary, Cyg X-2, as a background light source, a mystery came about
when the putatively strong OVII Kalpha line was not detected in Chandra grating
observations, while other normally weaker lines such as OVII Kbeta as well as
OVI and OVIII Kalpha are clearly present (Yao et al. 2009). We have
investigated the grating spectra of Cyg X-2 from 10 XMM-Newton observations, in
search of the missing line. We detect it consistently in nine of these
observations, but the line is absent in the remaining one observation or is
inconsistent with the detection in others at a 4sigma confidence level. This
absence of the line resembles that seen in the Chandra observations. Similarly,
the OVI Kalpha line is found to disappear occasionally, but not in concert with
the variation of the OVII Kalpha line. All these variations are most likely due
to the presence of changing OVII and OVI Kalpha emission lines of Cyg X-2,
which are blurred together with the absorption ones in the X-ray spectra. A
re-examination of the Chandra grating data indeed shows evidence for a narrow
emission line slightly off the OVI Kalpha absorption line. We further show that
narrow NV emission lines with varying centroids and fluxes are present in
far-UV spectra from the Cosmic Origins Spectrograph aboard the Hubble Space
Telescope. These results provide new constraints on the accretion around the
neutron star and on the X-ray-heating of the stellar companion. The
understanding of these physical processes is also important to the fidelity of
using such local X-ray binaries for interstellar absorption line spectroscopy.
The hot interstellar medium is an important part of the Galactic ecosystem
and can be effectively characterized through X-ray absorption line
spectroscopy. However, in a study of the hot medium using the accreting neutron
star X-ray binary, Cyg X-2, as a background light source, a mystery came about
when the putatively strong OVII Kalpha line was not detected in Chandra grating
observations, while other normally weaker lines such as OVII Kbeta as well as
OVI and OVIII Kalpha are clearly present (Yao et al. 2009). We have
investigated the grating spectra of Cyg X-2 from 10 XMM-Newton observations, in
search of the missing line. We detect it consistently in nine of these
observations, but the line is absent in the remaining one observation or is
inconsistent with the detection in others at a 4sigma confidence level. This
absence of the line resembles that seen in the Chandra observations. Similarly,
the OVI Kalpha line is found to disappear occasionally, but not in concert with
the variation of the OVII Kalpha line. All these variations are most likely due
to the presence of changing OVII and OVI Kalpha emission lines of Cyg X-2,
which are blurred together with the absorption ones in the X-ray spectra. A
re-examination of the Chandra grating data indeed shows evidence for a narrow
emission line slightly off the OVI Kalpha absorption line. We further show that
narrow NV emission lines with varying centroids and fluxes are present in
far-UV spectra from the Cosmic Origins Spectrograph aboard the Hubble Space
Telescope. These results provide new constraints on the accretion around the
neutron star and on the X-ray-heating of the stellar companion. The
understanding of these physical processes is also important to the fidelity of
using such local X-ray binaries for interstellar absorption line spectroscopy.
Measurement of the Radius of Neutron Stars with High S/N Quiescent Low-mass X-ray Binaries in Globular Clusters. (arXiv:1302.0023v1 [astro-ph.HE])
Measurement of the Radius of Neutron Stars with High S/N Quiescent Low-mass X-ray Binaries in Globular Clusters. (arXiv:1302.0023v1 [astro-ph.HE]):
This paper presents the measurement of the neutron star (NS) radius using the
thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular
clusters (GCs). Recent observations of NSs have presented evidence that cold
ultra dense matter -- present in the core of NSs -- is best described by
"normal matter" equations of state (EoSs). Such EoSs predict that the radii of
NSs, Rns, are quasi-constant (within measurement errors, of ~10%) for
astrophysically relevant masses (Mns > 0.5 Msun). The present work adopts this
theoretical prediction as an assumption, and uses it to constrain a single Rns
value from five qLMXB targets with available high signal-to-noise X-ray
spectroscopic data. Employing a Markov-Chain Monte-Carlo approach, we produce
the marginalized posterior distribution for Rns, constrained to be the same
value for all five NSs in the sample. An effort was made to include all
quantifiable sources of uncertainty into the uncertainty of the quoted radius
measurement. These include the uncertainties in the distances to the GCs, the
uncertainties due to the Galactic absorption in the direction of the GCs, and
the possibility of a hard power-law spectral component for count excesses at
high photon energy, which are observed in some qLMXBs in the Galactic plane.
Using conservative assumptions,we found that the radius, common to the five
qLMXBs and constant for a wide range of masses, lies in the low range of
possible NS radii, Rns=9.1(+1.3)(-1.5) km (90%-confidence). Such a value is
consistent with low-res equations of state. We compare this result with
previous radius measurements of NSs from various analyses of different types of
systems. In addition, we compare the spectral analyses of individual qLMXBs to
previous works.
This paper presents the measurement of the neutron star (NS) radius using the
thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular
clusters (GCs). Recent observations of NSs have presented evidence that cold
ultra dense matter -- present in the core of NSs -- is best described by
"normal matter" equations of state (EoSs). Such EoSs predict that the radii of
NSs, Rns, are quasi-constant (within measurement errors, of ~10%) for
astrophysically relevant masses (Mns > 0.5 Msun). The present work adopts this
theoretical prediction as an assumption, and uses it to constrain a single Rns
value from five qLMXB targets with available high signal-to-noise X-ray
spectroscopic data. Employing a Markov-Chain Monte-Carlo approach, we produce
the marginalized posterior distribution for Rns, constrained to be the same
value for all five NSs in the sample. An effort was made to include all
quantifiable sources of uncertainty into the uncertainty of the quoted radius
measurement. These include the uncertainties in the distances to the GCs, the
uncertainties due to the Galactic absorption in the direction of the GCs, and
the possibility of a hard power-law spectral component for count excesses at
high photon energy, which are observed in some qLMXBs in the Galactic plane.
Using conservative assumptions,we found that the radius, common to the five
qLMXBs and constant for a wide range of masses, lies in the low range of
possible NS radii, Rns=9.1(+1.3)(-1.5) km (90%-confidence). Such a value is
consistent with low-res equations of state. We compare this result with
previous radius measurements of NSs from various analyses of different types of
systems. In addition, we compare the spectral analyses of individual qLMXBs to
previous works.
High redshift blazars. (arXiv:1302.0011v1 [astro-ph.CO])
High redshift blazars. (arXiv:1302.0011v1 [astro-ph.CO]):
Blazars are sources whose jet is pointing to us. Since their jets are
relativistic, the flux is greatly amplified in the direction of motion, making
blazars the most powerful persistent objects in the Universe. This is true at
all frequencies, but especially where their spectrum peaks. Although the
spectrum of moderate powerful sources peaks in the ~GeV range, extremely
powerful sources at high redshifts peak in the ~MeV band. This implies that the
hard X-ray band is the optimal one to find powerful blazars beyond a redshift
of ~4. First indications strongly suggest that powerful high-z blazars harbor
the most massive and active early black holes, exceeding a billion solar
masses. Since for each detected blazars there must exist hundreds of similar,
but misaligned, sources, the search for high-z blazars is becoming competitive
with the search of early massive black holes using radio-quiet quasars. Finding
how the two populations of black holes (one in jetted sources, the other in
radio-quiet objects) evolve in redshift will shed light on the growth of the
most massive black holes and possibly on the feedback between the central
engine and the rest of the host galaxy.
Blazars are sources whose jet is pointing to us. Since their jets are
relativistic, the flux is greatly amplified in the direction of motion, making
blazars the most powerful persistent objects in the Universe. This is true at
all frequencies, but especially where their spectrum peaks. Although the
spectrum of moderate powerful sources peaks in the ~GeV range, extremely
powerful sources at high redshifts peak in the ~MeV band. This implies that the
hard X-ray band is the optimal one to find powerful blazars beyond a redshift
of ~4. First indications strongly suggest that powerful high-z blazars harbor
the most massive and active early black holes, exceeding a billion solar
masses. Since for each detected blazars there must exist hundreds of similar,
but misaligned, sources, the search for high-z blazars is becoming competitive
with the search of early massive black holes using radio-quiet quasars. Finding
how the two populations of black holes (one in jetted sources, the other in
radio-quiet objects) evolve in redshift will shed light on the growth of the
most massive black holes and possibly on the feedback between the central
engine and the rest of the host galaxy.
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