417 research outputs found
Constraining the thermal history of the Warm-Hot Intergalactic Medium
We have identified a large-scale structure traced by galaxies at z=0.8,
within the Lockman Hole, by means of multi-object spectroscopic observations.
By using deep XMM images we have investigated the soft X-ray emission from the
Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this
large-scale structure and we set a tight upper limit to its flux in the very
soft 0.2-0.4 keV band. The non-detection requires the WHIM at these redshifts
to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower
redshift, our result indicates that the WHIM temperature is rapidly decreasing
with redshift, as expected in popular cosmological models.Comment: 10 pages, 5 figures, 1 appendix. A&A accepte
The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample
We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S(8-24 keV) = 7 x 10^(-14) erg s^(-1) cm^(-2 in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z = 0-2.1 (median (z) = 0.58). The spectral analysis is performed over the broad 0.5–24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at 〉 10 keV to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (N_H), reflection parameter (R), and 10–40 keV luminosity (L_X). Heavily obscured (log[N_H/cm^(-2] ≥ 23) and Compton-thick (CT; log[N_H/cm^(-2)] ≥ 24) AGN constitute ~25% (15–17 sources) and ~2–3% (1–2 sources) of the sample, respectively. The observed N_H distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of N_H, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to log[N_H/cm^(-2] = 20-24 AGN is poorly constrained, formally in the range 2–56% (90% upper limit of 66%). We derived a fraction (f_(abs)) of obscured AGN (log[N_H/cm^(-2]= 22-24) as a function of L_X in agreement with CXBPSM and previous z 〈 1 X-ray determinations. Furthermore, f_(abs) at z = 0.1-0.5 and log(L_x/erg s^(-1) ≈ 43.6-44.3 agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with L_X (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values
Studying the WHIM Content of the Galaxy Large-Scale Structures along the Line of Sight to H 2356-309
We make use of a 500ks Chandra HRC-S/LETG spectrum of the blazar H2356-309,
combined with a lower S/N spectrum of the same target, to search for the
presence of warm-hot absorbing gas associated with two Large-Scale Structures
(LSSs) crossed by this sightline at z=0.062 (the Pisces-Cetus Supercluster,
PCS) and at z=0.128 ("Farther Sculptor Wall", FSW). No statistically
significant (>=3sigma) individual absorption is detected from any of the strong
He- or H-like transitions of C, O and Ne at the redshifts of the structures.
However we are still able to constrain the physical and geometrical parameters
of the associated putative absorbing gas, by performing joint spectral fit of
marginal detections and upper limits of the strongest expected lines with our
self-consistent hybrid ionization WHIM spectral model. At the redshift of the
PCS we identify a warm phase with logT=5.35_-0.13^+0.07 K and log N_H
=19.1+/-0.2 cm^-2 possibly coexisting with a hotter and less significant phase
with logT=6.9^+0.1_-0.8 K and log N_H=20.1^+0.3_-1.7 cm^-2 (1sigma errors). For
the FSW we estimate logT=6.6_-0.2^+0.1 K and log N_H=19.8_-0.8^+0.4 cm^-2. Our
constraints allow us to estimate the cumulative number density per unit
redshifts of OVII WHIM absorbers. We also estimate the cosmological mass
density obtaining Omega_b(WHIM)=(0.021^+0.031_-0.018) (Z/Z_sun)^-1, consistent
with the mass density of the intergalactic 'missing baryons' for high
metallicities.Comment: 29 pages, 8 figures, 4 tables. Accepted for publication in Ap
The multi-phase winds of Markarian 231: from the hot, nuclear, ultra-fast wind to the galaxy-scale, molecular outflow
We present the best sensitivity and angular resolution maps of the molecular
disk and outflow of Mrk 231, as traced by CO observations obtained with
IRAM/PdBI, and we analyze archival Chandra and NuSTAR observations. We
constrain the physical properties of both the molecular disk and outflow, the
presence of a highly-ionized ultra-fast nuclear wind, and their connection. The
molecular outflow has a size of ~1 kpc, and extends in all directions around
the nucleus, being more prominent along the south-west to north-east direction,
suggesting a wide-angle biconical geometry. The maximum projected velocity of
the outflow is nearly constant out to ~1 kpc, thus implying that the density of
the outflowing material decreases from the nucleus outwards as . This
suggests that either a large part of the gas leaves the flow during its
expansion or that the bulk of the outflow has not yet reached out to ~1 kpc,
thus implying a limit on its age of ~1 Myr. We find and erg s.
Remarkably, our analysis of the X-ray data reveals a nuclear ultra-fast outflow
(UFO) with velocity -20000 km s, , and momentum load .We find as predicted for outflows undergoing an energy
conserving expansion. This suggests that most of the UFO kinetic energy is
transferred to mechanical energy of the kpc-scale outflow, strongly supporting
that the energy released during accretion of matter onto super-massive black
holes is the ultimate driver of giant massive outflows. We estimate a momentum
boost . The ratios and agree
with the requirements of the most popular models of AGN feedback.Comment: 16 pages, 17 figures. Accepted for publication in A&
The X-Ray Concentration-Virial Mass Relation
We present the concentration (c)-virial mass (M) relation of 39 galaxy
systems ranging in mass from individual early-type galaxies up to the most
massive galaxy clusters, (0.06-20) x 10^{14} M_sun. We selected for analysis
the most relaxed systems possessing the highest quality data currently
available in the Chandra and XMM public data archives. A power-law model fitted
to the X-ray c-M relation requires at high significance (6.6 sigma) that c
decreases with increasing M, which is a general feature of CDM models. The
median and scatter of the c-M relation produced by the flat, concordance LCDM
model (Omega_m=0.3, sigma_8=0.9) agrees with the X-ray data provided the sample
is comprised of the most relaxed, early forming systems, which is consistent
with our selection criteria. Holding the rest of the cosmological parameters
fixed to those in the concordance model the c-M relation requires 0.76< sigma_8
<1.07 (99% conf.), assuming a 10% upward bias in the concentrations for early
forming systems. The tilted, low-sigma_8 model suggested by a new WMAP analysis
is rejected at 99.99% confidence, but a model with the same tilt and
normalization can be reconciled with the X-ray data by increasing the dark
energy equation of state parameter to w ~ -0.8. When imposing the additional
constraint of the tight relation between sigma_8 and Omega_m from studies of
cluster abundances, the X-ray c-M relation excludes (>99% conf.) both open CDM
models and flat CDM models with Omega_m ~1. This result provides novel evidence
for a flat, low-Omega_m universe with dark energy using observations only in
the local (z << 1) universe. Possible systematic errors in the X-ray mass
measurements of a magnitude ~10% suggested by CDM simulations do not change our
conclusions.Comment: Accepted for Publication in ApJ; 13 pages, 4 figures; minor
clarifications and updates; correlation coefficients corrected in Table 1
(correct values were used in the analysis in previous versions); conclusions
unchange
The dense molecular gas in the QSO SDSS J231038.88+185519.7 resolved by ALMA
We present ALMA observations of the CO(6-5) and [CII] emission lines and the
sub-millimeter continuum of the quasi-stellar object (QSO) SDSS
J231038.88+185519.7. Compared to previous studies, we have analyzed a synthetic
beam that is ten times smaller in angular size, we have achieved ten times
better sensitivity in the CO(6-5) line, and two and half times better
sensitivity in the [CII] line, enabling us to resolve the molecular gas
emission. We obtain a size of the dense molecular gas of kpc, and
of kpc for the 91.5 GHz dust continuum. By assuming that CO(6-5) is
thermalized, and by adopting a CO--to-- conversion factor , we infer a molecular gas mass of
. Assuming that the
observed CO velocity gradient is due to an inclined rotating disk, we derive a
dynamical mass of , which is a factor of approximately two smaller than the previously
reported estimate based on [CII]. Regarding the central black hole, we provide
a new estimate of the black hole mass based on the C~IV emission line detected
in the X-SHOOTER/VLT spectrum: . We find a molecular gas fraction of ,
where . We derive a ratio
suggesting high gas turbulence, outflows/inflows
and/or complex kinematics due to a merger event. We estimate a global Toomre
parameter , indicating likely cloud fragmentation. We compare,
at the same angular resolution, the CO(6-5) and [CII] distributions, finding
that dense molecular gas is more centrally concentrated with respect to [CII].
We find that the current BH growth rate is similar to that of its host galaxy.Comment: A&A in pres
The Absence of Adiabatic Contraction of the Radial Dark Matter Profile in the Galaxy Cluster A2589
We present an X-ray analysis of the radial mass profile of the radio-quiet
galaxy cluster A2589 between 0.015-0.25 r_vir using an XMM-Newton observation.
Except for a ~16 kpc shift of the X-ray center of the R=45-60 kpc annulus,
A2589 possesses a remarkably symmetrical X-ray image and is therefore an
exceptional candidate for precision studies of its mass profile by applying
hydrostatic equilibrium. The total gravitating matter profile is well described
by the NFW model (fractional residuals <~10%) with c_vir=6.1 +/- 0.3 and M_vir
= 3.3 +/- 0.3 x 10^{14} M_sun (r_vir = 1.74 +/- 0.05 Mpc) in excellent
agreement with LCDM. When the mass of the hot ICM is subtracted from the
gravitating matter profile, the NFW model fitted to the resulting dark matter
(DM) profile produces essentially the same result. However, if a component
accounting for the stellar mass (M_*) of the cD galaxy is included, then the
NFW fit to the DM profile is substantially degraded in the central r ~50 kpc
for reasonable M_*/L_V. Modifying the NFW DM halo by adiabatic contraction
arising from the early condensation of stellar baryons in the cD galaxy further
degrades the fit. The fit is improved substantially with a Sersic-like model
recently suggested by high resolution N-body simulations but with an inverse
Sersic index, alpha ~0.5, a factor of ~3 higher than predicted. We argue that
neither random turbulent motions nor magnetic fields can provide sufficient
non-thermal pressure support to reconcile the XMM mass profile with adiabatic
contraction of a CDM halo assuming reasonable M_*/L_V. Our results support the
scenario where, at least for galaxy clusters, processes during halo formation
counteract adiabatic contraction so that the total gravitating mass in the core
approximately follows the NFW profile.Comment: 15 pages, 11 figures, accepted for publication in ApJ. Minor changes
to match published versio
Mass assembly and AGN activity at in the dense environment of XDCPJ0044.0-2033
XDCP0044.0-2033 is the most massive galaxy cluster known at z>1.5 and its
core shows a high density of galaxies which are experiencing mergers and
hosting nuclear activity. We present a multi-wavelength study of a region
located 157 kpc from the center of this galaxy cluster, for which we have
photometric and spectroscopic multi-wavelength observations (high resolution
HST images in F105W, F140W and F160W bands, NIR KMOS data in H and YJ bands and
Chandra ACIS-S X-ray data). Our main goal is to investigate the environmental
effects acting on the galaxies inhabiting this high density region. We find
that the analyzed region hosts at least nine different sources, six of them
confirmed to be cluster members within a narrow redshift range 1.5728<z<1.5762.
These sources form two different complexes at a projected distance of 13
kpc, which are undergoing merging on an estimated timescale off 10-30 Myr. One
of the sources shows the presence of a broad H alpha emission line and is
classified as Type 1 AGN. This AGN is associated to an X-ray point-like source,
whose emission appears moderately obscured (with intrinsic absorption ) and hosts a relatively massive black hole with mass
, which is accreting with an Eddington ratio of
0.2. We conclude that the analyzed region is consistent with being the
formation site of a secondary BCG. These findings, together with an in-depth
analysis the X-ray morphology of the cluster, suggest a merging scenario of the
entire cluster, with two massive halos both harbouring two rapidly evolving
BCGs on the verge of being assembled. Our results are also consistent with the
scenario in which the AGN phase in member galaxies is triggered by gas-rich
mergers, playing a relevant role in the formation of the red sequence of
elliptical galaxies observed in the center of local galaxy clusters
The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample
We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S(8-24 keV) = 7 x 10^(-14) erg s^(-1) cm^(-2 in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z = 0-2.1 (median (z) = 0.58). The spectral analysis is performed over the broad 0.5–24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at 〉 10 keV to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (N_H), reflection parameter (R), and 10–40 keV luminosity (L_X). Heavily obscured (log[N_H/cm^(-2] ≥ 23) and Compton-thick (CT; log[N_H/cm^(-2)] ≥ 24) AGN constitute ~25% (15–17 sources) and ~2–3% (1–2 sources) of the sample, respectively. The observed N_H distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of N_H, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to log[N_H/cm^(-2] = 20-24 AGN is poorly constrained, formally in the range 2–56% (90% upper limit of 66%). We derived a fraction (f_(abs)) of obscured AGN (log[N_H/cm^(-2]= 22-24) as a function of L_X in agreement with CXBPSM and previous z 〈 1 X-ray determinations. Furthermore, f_(abs) at z = 0.1-0.5 and log(L_x/erg s^(-1) ≈ 43.6-44.3 agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with L_X (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values
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