Active galaxy 4U 1344-60: did the relativistic line disappear?. (arXiv:1209.4068v1 [astro-ph.HE]):
X-ray bright active galactic nuclei represent a unique astrophysical
laboratory for studying accretion physics around super-massive black holes. 4U
1344-60 is a bright Seyfert galaxy which revealed relativistic reflection
features in the archival XMM-Newton observation. We present the spectroscopic
results of new data obtained with the Suzaku satellite and compare them with
the previous XMM-Newton observation. The X-ray continuum of 4U 1344-60 can be
well described by a power-law component with the photon index ~ 1.7 modified by
a fully and a partially covering local absorbers. We measured a substantial
decrease of the fraction of the partially absorbed radiation from around 45% in
the XMM-Newton observation to less than 10% in the Suzaku observation while the
power-law slope remains constant within uncertainties. The iron line in the
Suzaku spectrum is relatively narrow, $\sigma=(0.08 \pm 0.02)$ keV, without any
suggestion for relativistic broadening. Regarding this, we interpret the iron
line in the archival XMM-Newton spectrum as a narrow line of the same width
plus an additional red-shifted emission around 6.1 keV. No evidence of the
relativistic reflection is present in the Suzaku spectra. The detected
red-shifted iron line during the XMM-Newton observation could be a temporary
feature either due to locally enhanced emission or decreased ionisation in the
innermost accretion flow.
Monday, September 24, 2012
Measuring the Ultimate Mass of Galaxy Clusters: Redshifts and Mass Profiles from the Hectospec Cluster Survey (HeCS). (arXiv:1209.3786v1 [astro-ph.CO])
Measuring the Ultimate Mass of Galaxy Clusters: Redshifts and Mass Profiles from the Hectospec Cluster Survey (HeCS). (arXiv:1209.3786v1 [astro-ph.CO]):
The infall regions of galaxy clusters represent the largest gravitationally
bound structures in a $\Lambda$CDM universe. Measuring cluster mass profiles
into the infall regions provides an estimate of the ultimate mass of these
haloes. We use the caustic technique to measure cluster mass profiles from
galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an
extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey
58 clusters selected by X-ray flux at 0.1${body}lt;$z$<$0.3. The survey includes
21,314 unique MMT/Hectospec redshifts for individual galaxies; 10,275 of these
galaxies are cluster members. For each cluster we acquired high signal-to-noise
spectra for $\sim 200$ cluster members and a comparable number of
foreground/background galaxies. The cluster members trace out infall patterns
around the clusters. The members define a very narrow red sequence. The
velocity dispersions decline with radius; we demonstrate that the determination
of the velocity dispersion is insensitive to the inclusion of bluer members (a
small fraction of the cluster population). We apply the caustic technique to
define membership and estimate the mass profiles to large radii. The ultimate
halo mass of clusters (the mass that remains bound in the far future of a
$\Lambda$CDM universe) is on average (1.99$\pm$0.11)$M_{200}$, a new
observational cosmological test in essential agreement with simulations. Summed
profiles binned in $M_{200}$ and in $L_X$ demonstrate that the predicted NFW
form of the density profile is a remarkably good representation of the data in
agreement with weak lensing results extending to large radius. The
concentration of these summed profiles is also consistent with theoretical
predictions.
The infall regions of galaxy clusters represent the largest gravitationally
bound structures in a $\Lambda$CDM universe. Measuring cluster mass profiles
into the infall regions provides an estimate of the ultimate mass of these
haloes. We use the caustic technique to measure cluster mass profiles from
galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an
extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey
58 clusters selected by X-ray flux at 0.1${body}lt;$z$<$0.3. The survey includes
21,314 unique MMT/Hectospec redshifts for individual galaxies; 10,275 of these
galaxies are cluster members. For each cluster we acquired high signal-to-noise
spectra for $\sim 200$ cluster members and a comparable number of
foreground/background galaxies. The cluster members trace out infall patterns
around the clusters. The members define a very narrow red sequence. The
velocity dispersions decline with radius; we demonstrate that the determination
of the velocity dispersion is insensitive to the inclusion of bluer members (a
small fraction of the cluster population). We apply the caustic technique to
define membership and estimate the mass profiles to large radii. The ultimate
halo mass of clusters (the mass that remains bound in the far future of a
$\Lambda$CDM universe) is on average (1.99$\pm$0.11)$M_{200}$, a new
observational cosmological test in essential agreement with simulations. Summed
profiles binned in $M_{200}$ and in $L_X$ demonstrate that the predicted NFW
form of the density profile is a remarkably good representation of the data in
agreement with weak lensing results extending to large radius. The
concentration of these summed profiles is also consistent with theoretical
predictions.
Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*. (arXiv:1209.4599v1 [astro-ph.HE])
Self-consistent spectra from radiative GRMHD simulations of accretion onto Sgr A*. (arXiv:1209.4599v1 [astro-ph.HE]):
We present the first spectral energy distributions produced self-consistently
by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical
simulations, where radiative cooling is included in the dynamical calculation.
As a case study, we focus on the accretion flow around the supermassive black
hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best
constrained physical parameters. We compare the simulated spectra to the
observational data of Sgr A* and explore the parameter space of our model to
determine the effect of changing the initial magnetic field configuration, ion
to electron temperature ratio T_i/T_e and the target accretion rate. We find
the best description of the data for a mass accretion rate of ~ 1e-9 Msun/yr,
and rapid spin (0.7 < a_* < 0.9). The submillimeter peak flux seems largely
independent of initial conditions, while the higher energies can be very
sensitive to the initial magnetic field configuration. Finally, we also discuss
flaring features observed in some simulations, that may be due to artifacts of
the 2D configuration.
We present the first spectral energy distributions produced self-consistently
by 2.5D general relativistic magneto-hydrodynamical (GRMHD) numerical
simulations, where radiative cooling is included in the dynamical calculation.
As a case study, we focus on the accretion flow around the supermassive black
hole in the Galactic Centre, Sagittarius A* (Sgr A*), which has the best
constrained physical parameters. We compare the simulated spectra to the
observational data of Sgr A* and explore the parameter space of our model to
determine the effect of changing the initial magnetic field configuration, ion
to electron temperature ratio T_i/T_e and the target accretion rate. We find
the best description of the data for a mass accretion rate of ~ 1e-9 Msun/yr,
and rapid spin (0.7 < a_* < 0.9). The submillimeter peak flux seems largely
independent of initial conditions, while the higher energies can be very
sensitive to the initial magnetic field configuration. Finally, we also discuss
flaring features observed in some simulations, that may be due to artifacts of
the 2D configuration.
A massive bubble of extremely metal poor gas around a collapsing Ly-alpha blob at z=2.54. (arXiv:1209.4676v1 [astro-ph.CO])
A massive bubble of extremely metal poor gas around a collapsing Ly-alpha blob at z=2.54. (arXiv:1209.4676v1 [astro-ph.CO]):
Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio
Canarias, we have examined the gaseous environment of the radio-loud quasar TXS
1436+157 (z=2.54), previously known to be associated with a large Ly-alpha
nebula and a spatially extended Ly-alpha-absorbing structure. From the Ly-alpha
nebula we measure kinematic properties consistent with infall at a rate of
about 10-100 M./yr - more than sufficient to power a quasar at the top of the
luminosity function. The absorbing structure lies outside of the Ly-alpha
nebula, at a radius of >40 kpc from the quasar. Against the bright unresolved
continuum and line emission from the quasar, we detect in absorption the NV
1239,1241, CIV 1548,1551 and SiIV 1394,1403 doublets, with no unambiguous
detection of absorption lines from any low-ionization species of metal. The
metal column densities, taken together with the HI column density measurement
from the literature, indicate that the absorbing gas is predominantly ionized
by the quasar, has a mass of hydrogen of >1.6 x 10E11 M., a gas density of <18
per cubic cm, a line of sight thickness of >18 pc, and a covering factor
approaching unity. While this absorbing structure is clearly not composed of
pristine gas, it has an extremely low metallicity, with ionization models
providing a 3-sigma limit of 12+log(O/H)<7.3. To explain these results, we
discuss a scenario involving starburst-driven super-bubbles and the creation of
infalling filaments of cold gas which fuel/trigger the quasar. We also discuss
the possibility of detecting large-scale absorbers such as this in emission
when illuminated by a powerful quasar.
Using long-slit optical spectroscopy obtained at the 10.4 m Gran Telescopio
Canarias, we have examined the gaseous environment of the radio-loud quasar TXS
1436+157 (z=2.54), previously known to be associated with a large Ly-alpha
nebula and a spatially extended Ly-alpha-absorbing structure. From the Ly-alpha
nebula we measure kinematic properties consistent with infall at a rate of
about 10-100 M./yr - more than sufficient to power a quasar at the top of the
luminosity function. The absorbing structure lies outside of the Ly-alpha
nebula, at a radius of >40 kpc from the quasar. Against the bright unresolved
continuum and line emission from the quasar, we detect in absorption the NV
1239,1241, CIV 1548,1551 and SiIV 1394,1403 doublets, with no unambiguous
detection of absorption lines from any low-ionization species of metal. The
metal column densities, taken together with the HI column density measurement
from the literature, indicate that the absorbing gas is predominantly ionized
by the quasar, has a mass of hydrogen of >1.6 x 10E11 M., a gas density of <18
per cubic cm, a line of sight thickness of >18 pc, and a covering factor
approaching unity. While this absorbing structure is clearly not composed of
pristine gas, it has an extremely low metallicity, with ionization models
providing a 3-sigma limit of 12+log(O/H)<7.3. To explain these results, we
discuss a scenario involving starburst-driven super-bubbles and the creation of
infalling filaments of cold gas which fuel/trigger the quasar. We also discuss
the possibility of detecting large-scale absorbers such as this in emission
when illuminated by a powerful quasar.
X-ray observations of the merging cluster CIZA J2242.8+5301. (arXiv:1209.4642v1 [astro-ph.CO])
X-ray observations of the merging cluster CIZA J2242.8+5301. (arXiv:1209.4642v1 [astro-ph.CO]):
Multiwavelength studies of radio relics at merger shocks set powerful
constraints on the relics origin and formation mechanism. However, for X-ray
observations, a main difficulty is represented by the low X-ray surface
brightness far out in the cluster outskirts, where relics are typically found.
Here, we present XMM-Newton results from a 130-ks observation of CIZA
J2242.8+5301, a cluster at z=0.19 that hosts a double radio relic. We focus on
the well-defined northern relic. There is a difference of ~55% between the
temperature we measure behind the relic, and the temperature measured with
Suzaku. We analyse the reasons for this large discrepancy, and discuss the
possibility of reliably measuring the temperature beyond the northern relic.
Multiwavelength studies of radio relics at merger shocks set powerful
constraints on the relics origin and formation mechanism. However, for X-ray
observations, a main difficulty is represented by the low X-ray surface
brightness far out in the cluster outskirts, where relics are typically found.
Here, we present XMM-Newton results from a 130-ks observation of CIZA
J2242.8+5301, a cluster at z=0.19 that hosts a double radio relic. We focus on
the well-defined northern relic. There is a difference of ~55% between the
temperature we measure behind the relic, and the temperature measured with
Suzaku. We analyse the reasons for this large discrepancy, and discuss the
possibility of reliably measuring the temperature beyond the northern relic.
Ionized Gas in the First 10 Kiloparsecs of the Interstellar Galactic Halo: Metal Ion Fractions. (arXiv:1209.4640v1 [astro-ph.GA])
Ionized Gas in the First 10 Kiloparsecs of the Interstellar Galactic Halo: Metal Ion Fractions. (arXiv:1209.4640v1 [astro-ph.GA]):
We present direct measures of the ionization fractions of several sulfur ions
in the Galactic warm ionized medium (WIM). We obtained high resolution
ultraviolet absorption line spectroscopy of post-asymptotic giant branch stars
in the the globular clusters Messier 3 [(l,b)=(42.2, +78.7); d=10.2 kpc, z=10.0
kpc] and Messier 5 [(l,b)=(3.9, +46.8); d=7.5 kpc, z = +5.3 kpc] with the
Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure,
or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H
I. These clusters also house millisecond pulsars, whose dispersion measures
give an electron column density from which we infer the H II column in these
directions. We find fractions of S+2 in the WIM for the M 3 and M 5 sight lines
x(S+2) = N(S+2)/N(S) = 0.33+/-0.07 and 0.47+/-0.09, respectively, with
variations perhaps related to location. With negligible quantities of the
higher ionization states, we conclude S+ and S+2 account for all of the S in
the WIM. We extend the methodology to study the ion fractions in the warm and
hot ionized gas of the Milky Way, including the high ions Si+3, C+3, N+4, and
O+5. The vast majority of the Galactic ionized gas is warm (T ~ 10^4 K) and
photoionized (the WIM) or very hot (T > 4x10^5 K) and collisionally ionized.
The common tracer of ionized gas beyond the Milky Way, O+5, traces <1% of the
total ionized gas mass of the Milky Way.
We present direct measures of the ionization fractions of several sulfur ions
in the Galactic warm ionized medium (WIM). We obtained high resolution
ultraviolet absorption line spectroscopy of post-asymptotic giant branch stars
in the the globular clusters Messier 3 [(l,b)=(42.2, +78.7); d=10.2 kpc, z=10.0
kpc] and Messier 5 [(l,b)=(3.9, +46.8); d=7.5 kpc, z = +5.3 kpc] with the
Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure,
or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H
I. These clusters also house millisecond pulsars, whose dispersion measures
give an electron column density from which we infer the H II column in these
directions. We find fractions of S+2 in the WIM for the M 3 and M 5 sight lines
x(S+2) = N(S+2)/N(S) = 0.33+/-0.07 and 0.47+/-0.09, respectively, with
variations perhaps related to location. With negligible quantities of the
higher ionization states, we conclude S+ and S+2 account for all of the S in
the WIM. We extend the methodology to study the ion fractions in the warm and
hot ionized gas of the Milky Way, including the high ions Si+3, C+3, N+4, and
O+5. The vast majority of the Galactic ionized gas is warm (T ~ 10^4 K) and
photoionized (the WIM) or very hot (T > 4x10^5 K) and collisionally ionized.
The common tracer of ionized gas beyond the Milky Way, O+5, traces <1% of the
total ionized gas mass of the Milky Way.
Thursday, September 20, 2012
The high-redshift (z>3) AGN population in the 4 Ms Chandra Deep Field South. (arXiv:1209.4193v1 [astro-ph.CO])
The high-redshift (z>3) AGN population in the 4 Ms Chandra Deep Field South. (arXiv:1209.4193v1 [astro-ph.CO]):
We present results from a spectral analysis of a sample of high-redshift
(z>3) X-ray selected AGN in the 4 Ms Chandra Deep Field South (CDF-S), the
deepest X-ray survey to date. The sample is selected using the most recent
spectroscopic and photometric information available in this field. It consists
of 34 sources with median redshift z=3.7, 80 median net counts in the 0.5-7 keV
band and median rest-frame absorption-corrected luminosity $L_{2-10
\rmn{keV}}\approx1.5\times10^{44}\rmn{erg} \rmn{s^{-1}}$. Spectral analysis for
the full sample is presented and the intrinsic column density distribution,
corrected for observational biases using spectral simulations, is compared with
the expectations of X-ray background (XRB) synthesis models. We find that
$\approx57$ per cent of the sources are highly obscured
($N_H>10^{23}\rmn{cm^{-2}}$). Source number counts in the $0.5-2\rmn{keV}$ band
down to flux $F_{0.5-2 \rmn{keV}}\approx4\times10^{-17}\rmn{erg}
\rmn{s^{-1}cm^{-2}}$ are also presented. Our results are consistent with a
decline of the AGN space density at z>3 and suggest that, at those redshifts,
the AGN obscured fraction is in agreement with the expectations of XRB
synthesis models.
We present results from a spectral analysis of a sample of high-redshift
(z>3) X-ray selected AGN in the 4 Ms Chandra Deep Field South (CDF-S), the
deepest X-ray survey to date. The sample is selected using the most recent
spectroscopic and photometric information available in this field. It consists
of 34 sources with median redshift z=3.7, 80 median net counts in the 0.5-7 keV
band and median rest-frame absorption-corrected luminosity $L_{2-10
\rmn{keV}}\approx1.5\times10^{44}\rmn{erg} \rmn{s^{-1}}$. Spectral analysis for
the full sample is presented and the intrinsic column density distribution,
corrected for observational biases using spectral simulations, is compared with
the expectations of X-ray background (XRB) synthesis models. We find that
$\approx57$ per cent of the sources are highly obscured
($N_H>10^{23}\rmn{cm^{-2}}$). Source number counts in the $0.5-2\rmn{keV}$ band
down to flux $F_{0.5-2 \rmn{keV}}\approx4\times10^{-17}\rmn{erg}
\rmn{s^{-1}cm^{-2}}$ are also presented. Our results are consistent with a
decline of the AGN space density at z>3 and suggest that, at those redshifts,
the AGN obscured fraction is in agreement with the expectations of XRB
synthesis models.
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