The Impact of Suzaku Measurements on Astroparticle Physics. (arXiv:1211.1115v1 [astro-ph.CO]):
Results from the Suzaku X-ray broad-band observations of clusters of galaxies
are summarized. Aiming at understanding the physics of gas heating/particle
acceleration and the cluster dynamical evolution, we search for non-thermal
hard X-ray emission from merging clusters, particularly A2163 and the Bullet
Cluster, based on the Suzaku and XMM-Newton/Chandra joint analyzes. The
observed hard X-ray emission is well represented by the single- or
multi-temperature thermal models including super-hot (kT~20 keV) gas. On the
other hand, no significant non-thermal hard X-ray emission has been detected.
Together with the presently available literature, the hard X-ray properties
have been studied for about 10 clusters with Suzaku. The present status on
Suzaku measurements of non-thermal X-ray emission and the cluster magnetic
field are summarized and compared with those from the RXTE, BeppoSAX, and Swift
satellites. The future prospects are briefly mentioned.
Friday, November 9, 2012
X-ray properties of BzK-selected galaxies in the deepest X-ray fields. (arXiv:1211.1028v1 [astro-ph.GA])
X-ray properties of BzK-selected galaxies in the deepest X-ray fields. (arXiv:1211.1028v1 [astro-ph.GA]):
We investigate the X-ray properties of BzK-selected galaxies at z $\sim$ 2
using deep X-ray data in the Chandra Deep Field South and North (CDFS and
CDFN). Of these we directly detect in X-rays 49 sBzKs in CDFS and 32 sBzKs in
CDFN. Stacking the undetected sources also reveals a significant X-ray signal.
Investigating the X-ray detection rate and stacked flux versus the IR excess
parameter (i.e. SFRtotal/SFRUV,corr), we find no strong evidence for an
increased X-ray detection rate, or a harder X-ray spectrum in IR Excess sBzKs.
This is particularly the case when one accounts for the strong correlation
between the IR excess parameter and the bolometric IR luminosity (LIR), e.g.
when controlling for LIR, the IR Non-Excess sBzKs show a detection rate at
least as high. While both direct detections and stacking suggest that the AGN
fraction in sBzK galaxies is high, there is no clear evidence for widespread
Compton thick activity in either the sBzK population generally, or the IR
Excess sBzK subsample. The very hard X-ray signal obtained for the latter in
earlier work was most likely contaminated by a few hard X-ray sources now
directly detected in deeper X-ray data. The X-ray detection fraction of passive
BzK galaxies in our sample is if anything higher than that of sBZKs, so there
is no evidence for coeval black hole growth and star formation from X-ray
analysis of the BzK populations. Because increased AGN activity in the IR
excess population is not indicated by our X-ray analysis, it appears that the
bulk of the IR Excess sBzK population are luminous star-forming galaxies whose
SFRs are either overestimated at 24 microns, underestimated in the UV, or both.
This conclusion reinforces recent results from Herschel which show similar
effects.
We investigate the X-ray properties of BzK-selected galaxies at z $\sim$ 2
using deep X-ray data in the Chandra Deep Field South and North (CDFS and
CDFN). Of these we directly detect in X-rays 49 sBzKs in CDFS and 32 sBzKs in
CDFN. Stacking the undetected sources also reveals a significant X-ray signal.
Investigating the X-ray detection rate and stacked flux versus the IR excess
parameter (i.e. SFRtotal/SFRUV,corr), we find no strong evidence for an
increased X-ray detection rate, or a harder X-ray spectrum in IR Excess sBzKs.
This is particularly the case when one accounts for the strong correlation
between the IR excess parameter and the bolometric IR luminosity (LIR), e.g.
when controlling for LIR, the IR Non-Excess sBzKs show a detection rate at
least as high. While both direct detections and stacking suggest that the AGN
fraction in sBzK galaxies is high, there is no clear evidence for widespread
Compton thick activity in either the sBzK population generally, or the IR
Excess sBzK subsample. The very hard X-ray signal obtained for the latter in
earlier work was most likely contaminated by a few hard X-ray sources now
directly detected in deeper X-ray data. The X-ray detection fraction of passive
BzK galaxies in our sample is if anything higher than that of sBZKs, so there
is no evidence for coeval black hole growth and star formation from X-ray
analysis of the BzK populations. Because increased AGN activity in the IR
excess population is not indicated by our X-ray analysis, it appears that the
bulk of the IR Excess sBzK population are luminous star-forming galaxies whose
SFRs are either overestimated at 24 microns, underestimated in the UV, or both.
This conclusion reinforces recent results from Herschel which show similar
effects.
Sunyaev-Zel'dovich-Measured Pressure Profiles from the Bolocam X-ray/SZ Galaxy Cluster Sample. (arXiv:1211.1632v1 [astro-ph.CO])
Sunyaev-Zel'dovich-Measured Pressure Profiles from the Bolocam X-ray/SZ Galaxy Cluster Sample. (arXiv:1211.1632v1 [astro-ph.CO]):
We describe Sunyaev-Zel'dovich (SZ) effect measurements and analysis of the
intracluster medium (ICM) pressure profiles of a set of 45 massive galaxy
clusters imaged using Bolocam at the Caltech Submillimeter Observatory. We have
used masses determined from Chandra X-ray observations to scale each cluster's
profile by the overdensity radius R500 and the mass-and-redshift-dependent
normalization factor P500. We deproject the average pressure profile of our
sample into 13 logarithmically spaced radial bins between 0.07R500 and 3.5R500.
We find that a generalized Navarro, Frenk, and White (gNFW) profile describes
our data with sufficient goodness-of-fit and best-fit parameters (C500, alpha,
beta, gamma, P0 = 1.18, 0.86, 3.67, 0.67, 4.29). We also use the X-ray data to
define cool-core and disturbed subsamples of clusters, and we constrain the
average pressure profiles of each of these subsamples. We find that given the
precision of our data the average pressure profiles of disturbed and cool-core
clusters are consistent with one another at R>~0.15R500, with cool-core systems
showing indications of higher pressure at R<~0.15R500. In addition, for the
first time, we place simultaneous constraints on the mass scaling of cluster
pressure profiles, their ensemble mean profile, and their radius-dependent
intrinsic scatter between 0.1R500 and 2.0R500. The scatter among profiles is
minimized at radii between ~0.2R500 and ~0.5R500, with a value of ~20%. The
best-fit mass scaling has a power-law slope of 0.49, which is shallower than
the nominal prediction of 2/3 from self-similar hydrostatic equilibrium models.
These results for the intrinsic scatter and mass scaling are largely consistent
with previous analyses, most of which have relied heavily on X-ray derived
pressures of clusters at significantly lower masses and redshifts compared to
our sample.
We describe Sunyaev-Zel'dovich (SZ) effect measurements and analysis of the
intracluster medium (ICM) pressure profiles of a set of 45 massive galaxy
clusters imaged using Bolocam at the Caltech Submillimeter Observatory. We have
used masses determined from Chandra X-ray observations to scale each cluster's
profile by the overdensity radius R500 and the mass-and-redshift-dependent
normalization factor P500. We deproject the average pressure profile of our
sample into 13 logarithmically spaced radial bins between 0.07R500 and 3.5R500.
We find that a generalized Navarro, Frenk, and White (gNFW) profile describes
our data with sufficient goodness-of-fit and best-fit parameters (C500, alpha,
beta, gamma, P0 = 1.18, 0.86, 3.67, 0.67, 4.29). We also use the X-ray data to
define cool-core and disturbed subsamples of clusters, and we constrain the
average pressure profiles of each of these subsamples. We find that given the
precision of our data the average pressure profiles of disturbed and cool-core
clusters are consistent with one another at R>~0.15R500, with cool-core systems
showing indications of higher pressure at R<~0.15R500. In addition, for the
first time, we place simultaneous constraints on the mass scaling of cluster
pressure profiles, their ensemble mean profile, and their radius-dependent
intrinsic scatter between 0.1R500 and 2.0R500. The scatter among profiles is
minimized at radii between ~0.2R500 and ~0.5R500, with a value of ~20%. The
best-fit mass scaling has a power-law slope of 0.49, which is shallower than
the nominal prediction of 2/3 from self-similar hydrostatic equilibrium models.
These results for the intrinsic scatter and mass scaling are largely consistent
with previous analyses, most of which have relied heavily on X-ray derived
pressures of clusters at significantly lower masses and redshifts compared to
our sample.
Constraints of the compactness of the isolated neutron stars via X-ray phase-resolved spectroscopy. (arXiv:1211.1842v1 [astro-ph.SR])
Constraints of the compactness of the isolated neutron stars via X-ray phase-resolved spectroscopy. (arXiv:1211.1842v1 [astro-ph.SR]):
A model with a condensed iron surface and partially ionized hydrogen-thin
atmosphere allows us to fit simultaneously the observed general spectral shape
and the broad absorption feature (observed at 0.3 keV) in different spin phases
of the isolated neutron star RBS 1223. We constrain some physical properties of
the X-ray emitting areas, i.e. the temperatures (Tpole1 ~ 105eV, Tpole2 ~99eV),
magnetic field strengths Bpole1 ~ Bpole2 ~ 8.6x10^13G) at the poles, and their
distribution parameters (a1 ~ 0.61, a2 ~ 0.29, indicating an absence of strong
toroidal magnetic field component). In addition, we are able to place some
constraints on the geometry of the emerging X-ray emission and the
gravitational redshift (z ~0.16+0.03-0.01) of the isolated neutron star RBS
1223.
A model with a condensed iron surface and partially ionized hydrogen-thin
atmosphere allows us to fit simultaneously the observed general spectral shape
and the broad absorption feature (observed at 0.3 keV) in different spin phases
of the isolated neutron star RBS 1223. We constrain some physical properties of
the X-ray emitting areas, i.e. the temperatures (Tpole1 ~ 105eV, Tpole2 ~99eV),
magnetic field strengths Bpole1 ~ Bpole2 ~ 8.6x10^13G) at the poles, and their
distribution parameters (a1 ~ 0.61, a2 ~ 0.29, indicating an absence of strong
toroidal magnetic field component). In addition, we are able to place some
constraints on the geometry of the emerging X-ray emission and the
gravitational redshift (z ~0.16+0.03-0.01) of the isolated neutron star RBS
1223.
X-Ray Determination of the Variable Rate of Mass Accretion onto TW Hydrae. (arXiv:1211.1710v1 [astro-ph.SR])
X-Ray Determination of the Variable Rate of Mass Accretion onto TW Hydrae. (arXiv:1211.1710v1 [astro-ph.SR]):
Diagnostics of electron temperature (T_e), electron density (n_e), and
hydrogen column density (N_H) from the Chandra High Energy Transmission Grating
spectrum of He-like Ne IX in TW Hydrae (TW Hya), in conjunction with a
classical accretion model, allow us to infer the accretion rate onto the star
directly from measurements of the accreting material. The new method introduces
the use of the absorption of Ne IX lines as a measure of the column density of
the intervening, accreting material. On average, the derived mass accretion
rate for TW Hya is 1.5 x 10^{-9} M_{\odot} yr^{-1}, for a stellar magnetic
field strength of 600 Gauss and a filling factor of 3.5%. Three individual
Chandra exposures show statistically significant differences in the Ne IX line
ratios, indicating changes in N_H, T_e, and n_e by factors of 0.28, 1.6, and
1.3, respectively. In exposures separated by 2.7 days, the observations
reported here suggest a five-fold reduction in the accretion rate. This
powerful new technique promises to substantially improve our understanding of
the accretion process in young stars.
Diagnostics of electron temperature (T_e), electron density (n_e), and
hydrogen column density (N_H) from the Chandra High Energy Transmission Grating
spectrum of He-like Ne IX in TW Hydrae (TW Hya), in conjunction with a
classical accretion model, allow us to infer the accretion rate onto the star
directly from measurements of the accreting material. The new method introduces
the use of the absorption of Ne IX lines as a measure of the column density of
the intervening, accreting material. On average, the derived mass accretion
rate for TW Hya is 1.5 x 10^{-9} M_{\odot} yr^{-1}, for a stellar magnetic
field strength of 600 Gauss and a filling factor of 3.5%. Three individual
Chandra exposures show statistically significant differences in the Ne IX line
ratios, indicating changes in N_H, T_e, and n_e by factors of 0.28, 1.6, and
1.3, respectively. In exposures separated by 2.7 days, the observations
reported here suggest a five-fold reduction in the accretion rate. This
powerful new technique promises to substantially improve our understanding of
the accretion process in young stars.
Properties of gas clumps and gas clumping factor in the intra cluster medium. (arXiv:1211.1695v1 [astro-ph.CO])
Properties of gas clumps and gas clumping factor in the intra cluster medium. (arXiv:1211.1695v1 [astro-ph.CO]):
The spatial distribution of gas matter inside galaxy clusters is not
completely smooth, but may host gas clumps associated with substructures. These
overdense gas substructures are generally a source of unresolved bias of X-ray
observations towards high density gas, but their bright luminosity peaks may be
resolved sources within the ICM, that deep X-ray exposures may be (already)
capable to detect. In this paper we aim at investigating both features, using a
set of high-resolution cosmological simulations with ENZO. First, we monitor
how the bias by unresolved gas clumping may yield incorrect estimates of global
cluster parameters and affects the measurements of baryon fractions by X-ray
observations. We find that based on X-ray observations of narrow radial strips,
it is difficult to recover the real baryon fraction to better than 10 - 20
percent uncertainty. Second, we investigated the possibility of observing
bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock
X-ray observations for several instruments (XMM, Suzaku and ROSAT) and
extracted the statistics of potentially detectable bright clumps. Some of the
brightest clumps predicted by simulations may already have been already
detected in X- ray images with a large field of view. However, their small
projected size makes it difficult to prove their existence based on X-ray
morphology only. Preheating, AGN feedback and cosmic rays are found to have
little impact on the statistical properties of gas clumps.
The spatial distribution of gas matter inside galaxy clusters is not
completely smooth, but may host gas clumps associated with substructures. These
overdense gas substructures are generally a source of unresolved bias of X-ray
observations towards high density gas, but their bright luminosity peaks may be
resolved sources within the ICM, that deep X-ray exposures may be (already)
capable to detect. In this paper we aim at investigating both features, using a
set of high-resolution cosmological simulations with ENZO. First, we monitor
how the bias by unresolved gas clumping may yield incorrect estimates of global
cluster parameters and affects the measurements of baryon fractions by X-ray
observations. We find that based on X-ray observations of narrow radial strips,
it is difficult to recover the real baryon fraction to better than 10 - 20
percent uncertainty. Second, we investigated the possibility of observing
bright X-ray clumps in the nearby Universe (z<=0.3). We produced simple mock
X-ray observations for several instruments (XMM, Suzaku and ROSAT) and
extracted the statistics of potentially detectable bright clumps. Some of the
brightest clumps predicted by simulations may already have been already
detected in X- ray images with a large field of view. However, their small
projected size makes it difficult to prove their existence based on X-ray
morphology only. Preheating, AGN feedback and cosmic rays are found to have
little impact on the statistical properties of gas clumps.
A Deep X-ray View of the Hot Halo in the Edge-on Spiral Galaxy NGC 891. (arXiv:1211.1669v1 [astro-ph.CO])
A Deep X-ray View of the Hot Halo in the Edge-on Spiral Galaxy NGC 891. (arXiv:1211.1669v1 [astro-ph.CO]):
NGC 891 is a nearby edge-on galaxy that is similar to the Milky Way and has a
hot X-ray emitting halo that could arise from accretion, a galactic fountain,
or a combination of the two. The metallicity of the gas can help distinguish
between these models, and here we report on results that use 138 ks of archival
Chandra data and 92 ks of new XMM-Newton data to measure the temperature and
metallicity of the hot halo of the galaxy. We find good fits for a thermal
model with kT ~ 0.2 keV and Z ~ 0.1 solar, and rule out solar metallicity to
more than 99% confidence. This result suggests accretion from the intergalactic
medium as the origin for the hot halo. However, it is also possible to fit a
two-temperature thermal model with solar metallicity where kT_1 = 0.1 keV and
kT_2 = 0.25 keV. A consideration of the cooling rate and scale height prefers
the single-temperature model. We also find that the cooling rate in the hot gas
cannot explain the massive HI halo in the steady state. In addition, a galactic
fountain model cannot eject enough mass to account for the HI halo, and we
speculate that the neutral halo may be gas from a prior outflow that has since
cooled.
NGC 891 is a nearby edge-on galaxy that is similar to the Milky Way and has a
hot X-ray emitting halo that could arise from accretion, a galactic fountain,
or a combination of the two. The metallicity of the gas can help distinguish
between these models, and here we report on results that use 138 ks of archival
Chandra data and 92 ks of new XMM-Newton data to measure the temperature and
metallicity of the hot halo of the galaxy. We find good fits for a thermal
model with kT ~ 0.2 keV and Z ~ 0.1 solar, and rule out solar metallicity to
more than 99% confidence. This result suggests accretion from the intergalactic
medium as the origin for the hot halo. However, it is also possible to fit a
two-temperature thermal model with solar metallicity where kT_1 = 0.1 keV and
kT_2 = 0.25 keV. A consideration of the cooling rate and scale height prefers
the single-temperature model. We also find that the cooling rate in the hot gas
cannot explain the massive HI halo in the steady state. In addition, a galactic
fountain model cannot eject enough mass to account for the HI halo, and we
speculate that the neutral halo may be gas from a prior outflow that has since
cooled.
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