We present results from the deep XMM-Newton observations of the two brightest X-ray sources in the Chandra Deep Field South (CDFS), PID 203 (z=0.544) and PID 319 (z=0.742). The long exposure of 2.5 Ms over a 10 year period (net 4 yr with a 6 yr gap)
makes it possible to obtain high quality X-ray spectra of these two Type I AGN with X-ray luminosity of 10^44 erg/s, typical luminosity for low-redshift PG quasars, track their X-ray variability both in flux and spectral shape. Both sources showed X-ray flux variability of ~10-20 per cent in rms which is similar in the soft (0.5-2 keV) and hard (2-7 keV) bands. PID 203, which has evidence for optical extinction, shows modest amount of absorption (nH~1e21cm^-2) in the X-ray spectrum. Fe K emission is strongly detected in both objects with EW~0.2 keV. The lines in both objects are moderately broad and exhibit marginal evidence for variability in shape and flux, indicating that the bulk of the line emission come from their accretion disks rather than distant tori.
We present the first X-ray spectrum of a Hot dust-obscured galaxy (DOG), namely W1835+4355 at z ~ 2.3. Hot DOGs represent a very rare population of hyperluminous (>= 10^47 erg/s), dust-enshrouded objects at z > 2 recently discovered in the WISE All S
ky Survey. The 40 ks XMM-Newton spectrum reveals a continuum as flat (Gamma ~ 0.8) as typically seen in heavily obscured AGN. This, along with the presence of strong Fe Kalpha emission, clearly suggests a reflection-dominated spectrum due to Compton-thick absorption. In this scenario, the observed luminosity of L(2-10 keV) ~ 2 x 10^44 erg/s is a fraction (<10%) of the intrinsic one, which is estimated to be >~ 5 x 10^45 erg/s by using several proxies. The Herschel data allow us to constrain the SED up to the sub-mm band, providing a reliable estimate of the quasar contribution (~ 75%) to the IR luminosity as well as the amount of star formation (~ 2100 Msun/yr). Our results thus provide additional pieces of evidence that associate Hot DOGs with an exceptionally dusty phase during which luminous quasars and massive galaxies co-evolve and a very efficient and powerful AGN-driven feedback mechanism is predicted by models.
The obscured accretion phase in BH growth is a key ingredient in many models linking the AGN activity with the evolution of their host galaxy. At present, a complete census of obscured AGN is still missing. The purpose of this work is to assess the r
eliability of the [NeV] emission line at 3426 A to pick up obscured AGN up to z~1 by assuming that [NeV] is a reliable proxy of the intrinsic AGN luminosity and using moderately deep X-ray data to characterize the amount of obscuration. A sample of 69 narrow-line (Type 2) AGN at z=0.65-1.20 were selected from the 20k-zCOSMOS Bright galaxy sample on the basis of the presence of the [NeV] emission. The X-ray properties of these galaxies were then derived using the Chandra-COSMOS coverage of the field; the X-ray-to-[NeV] flux ratio, coupled with X-ray spectral and stacking analyses, was then used to infer whether Compton-thin or Compton-thick absorption were present in these sources. Then the [NeV] luminosity function was computed to estimate the space density of Compton-thick (CT) AGN at z~0.8. Twenty-three sources were detected by Chandra, and their properties are consistent with moderate obscuration (on average, ~a few 10^{22} cm^-2). The X-ray properties of the remaining 46 X-ray undetected Type 2 AGN were derived using X-ray stacking analysis. Current data indicate that a fraction as high as ~40% of the present sample is likely to be CT. The space density of CT AGN with logL_2-10keV>43.5 at z=0.83 is (9.1+/-2.1) 10^{-6} Mpc^{-3}, in good agreement with both XRB model expectations and the previously measured space density for objects in a similar redshift and luminosity range. We regard our selection technique for CT AGN as clean but not complete, since even a mild extinction in the NLR can suppress [NeV] emission. Therefore, our estimate of their space density should be considered as a lower limit.
A sample of 94 narrow line AGN with 0.65<z<1.20 has been selected from the 20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [NeV]3426 line. Taking advantage of the large amount of data available in the COSMOS field, the properties
of the [NeV]-selected Type-2 AGN have been investigated, focusing on their host galaxies, X-ray emission, and optical line flux ratios. Finally, the diagnostic developed by Gilli et al. (2010), based on the X-ray to [NeV] luminosity ratio, has been exploited to search for the more heavily obscured AGN. We found that [Ne v]-selected narrow line AGN have Seyfert 2-like optical spectra, although with emission line ratios diluted by a star-forming component. The ACS morphologies and stellar component in the optical spectra indicate a preference for our Type-2 AGN to be hosted in early-spirals with stellar masses greater than 10^(9.5-10)Msun, on average higher than those of the galaxy parent sample. The fraction of galaxies hosting [NeV]-selected obscured AGN increases with the stellar mass, reaching a maximum of about 3% at 2x10^11 Msun. A comparison with other selection techniques at z~1 shows that the detection of the [Ne v] line is an effective method to select AGN in the optical band, in particular the most heavily obscured ones, but can not provide by itself a complete census of AGN2. Finally, the high fraction of [NeV]-selected Type-2 AGN not detected in medium-deep Chandra observations (67%) is suggestive of the inclusion of Compton-thick sources in our sample. The presence of a population of heavily obscured AGN is corroborated by the X-ray to [NeV] ratio; we estimated, by mean of X-ray stacking technique and simulations, that the Compton-thick fraction in our sample of Type-2 AGN is 43+-4%, in good agreement with standard assumptions by the XRB synthesis models.
(abridged) The XMM-Newton survey in the Chandra Deep Field South (XMM-CDFS) aims at detecting and studying the spectral properties of a significant number of obscured and Compton-thick AGN. The large effective area of XMMin the 2--10 and 5--10 keV ba
nds, coupled with a 3.45 Ms nominal exposure time, allows us to build clean samples in both bands, and makes the XMM-CDFS the deepest XMM survey currently published in the 5--10 keV band. The large multi-wavelength and spectroscopic coverage of the CDFS area allows for an immediate and abundant scientific return. We present the data reduction of the XMM-CDFS observations, the method for source detection in the 2--10 and 5--10keV bands, and the resulting catalogues. A number of 339 and 137 sources are listed in the above bands with flux limits of 6.6e-16 and 9.5e-16 erg/s/cm^2, respectively. The flux limits at 50% of the maximum sky coverage are 1.8e-15 and 4.0e-15 erg/s/cm^2, respectively. The catalogues have been cross-correlated with the Chandra ones: 315 and 130 identifications have been found with a likelihood-ratio method, respectively. A number of 15 new sources, previously undetected by Chandra, is found; 5 of them lie in the 4 Ms area. Redshifts, either spectroscopic or photometric, are available for ~92% of the sources. The number counts in both bands are presented and compared to other works. The survey coverage has been calculated with the help of two extensive sets of simulations, one set per band. The simulations have been produced with a newly-developed simulator, written with the aim of the most careful reproduction of the background spatial properties. We present a detailed decomposition of the XMM background into its components: cosmic, particle, and residual soft protons.
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 photometr
ic 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 $L_{2-10 rmn{keV}}approx1.5times10^{44}rmn{erg} rmn{s^{-1}}$. 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 $0.5-2rmn{keV}$ band down to flux $F_{0.5-2 rmn{keV}}approx4times10^{-17}rmn{erg} rmn{s^{-1}cm^{-2}}$ 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 on a search of heavily obscured active galaxies z>1.7 using the rest-frame 9-20 keV excess for X-ray sources detected in the deep XMM-CDFS survey. Out of 176 sources selected with the conservative detection criteria (>8 sigma) in t
he first source catalogue of Ranalli et al., 46 objects lie in the redshift range of interest with the median redshift z~2.5. Their typical rest-frame 10-20 keV luminosity is 1e+44 erg/s, as observed. Among optically faint objects that lack spectroscopic redshift, four were found to be strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption features in their X-ray spectra were used to obtain X-ray spectroscopic redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5 keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20 keV excess and were found to be strongly absorbed X-ray sources with column density of nH > 0.6e+24 cm-2, including two possible Compton thick sources. While they are emitting at quasar luminosity, ~3/4 of the sample objects are found to be absorbed by nH > 1e+22 cm-2. A comparison with local AGN at the matched luminosity suggests an increasing trend of the absorbed source fraction for high-luminosity AGN towards high redshifts.
We report on our analysis of XMM-Newton observations of the Seyfert 2 galaxy ESO 138-G1 (z = 0.0091). These data reveal a complex spectrum in both its soft and hard portions. The 0.5-2 keV band is characterized by a strong soft-excess component with
several emission lines, as commonly observed in other narrow-line AGN. Above 3 keV, a power-law fit yields a very flat slope (Gamma ~0.35), along with the presence of a prominent line-like emission feature around ~6.4 keV. This indicates heavy obscuration along the line of sight to the nucleus. We find an excellent fit to the 3-10 keV continuum with a pure reflection model, which provides strong evidence of a Compton-thick screen, preventing direct detection of the intrinsic nuclear X-ray emission. Although a model consisting of a power law transmitted through an absorber with Nh ~2.5 x 10^{23} cm^-2 also provides a reasonable fit to the hard X-ray data, the equivalent width value of ~800 eV measured for the Fe Kalpha emission line is inconsistent with a primary continuum obscured by a Compton-thin column density. Furthermore, the ratio of 2-10 keV to de-reddened [OIII] fluxes for ESO 138-G1 agrees with the typical values reported for well-studied Compton-thick Seyfert galaxies. Finally, we also note that the upper limits to the 15-150 keV flux provided by Swift/BAT and INTEGRAL/IBIS seem to rule out the presence of a transmitted component of the nuclear continuum even in this very hard X-ray band, hence imply that the column density of the absorber could be as high as 10^{25} cm^-2. This makes ESO 138-G1 a very interesting, heavy Compton-thick AGN candidate for the next X-ray missions with spectroscopic and imaging capabilities above 10 keV.
We present a study of the multi-wavelength properties, from the mid-infrared to the hard X-rays, of a sample of 255 spectroscopically identified X-ray selected Type-2 AGN from the XMM-COSMOS survey. Most of them are obscured the X-ray absorbing colum
n density is determined by either X-ray spectral analyses (for the 45% of the sample), or from hardness ratios. Spectral Energy Distributions (SEDs) are computed for all sources in the sample. The average SEDs in the optical band is dominated by the host-galaxy light, especially at low X-ray luminosities and redshifts. There is also a trend between X-ray and mid-infrared luminosity: the AGN contribution in the infrared is higher at higher X-ray luminosities. We calculate bolometric luminosities, bolometric corrections, stellar masses and star formation rates (SFRs) for these sources using a multi-component modeling to properly disentangle the emission associated to stellar light from that due to black hole accretion. For 90% of the sample we also have the morphological classifications obtained with an upgraded version of the Zurich Estimator of Structural Types (ZEST+). We find that on average Type-2 AGN have lower bolometric corrections than Type-1 AGN. Moreover, we confirm that the morphologies of AGN host-galaxies indicate that there is a preference for these Type-2 AGN to be hosted in bulge-dominated galaxies with stellar masses greater than 10^10 solar masses.
We present a long (~76 ks) Chandra observation of IRAS 09104+4109, a hyper-luminous galaxy, optically classified as a Type 2 AGN hosted in a cD galaxy in a cluster at z=0.442. We also report on the results obtained by fitting its broad-band spectral
energy distribution. The Compton-thick nature of this source (which has been often referred to as an archetype of Compton-thick Type 2 quasars) was formerly claimed on the basis of its marginal detection in the PDS instrument onboard BeppoSAX, being then disputed using XMM-Newton data. Both Chandra analysis and optical/mid-IR spectral fitting are consistent with the presence of heavy (~1-5 10^{23} cm^{-2}) but not extreme (Compton-thick) obscuration. However, using the mid-IR and the [OIII] emission as proxies of the nuclear hard X-ray luminosity suggests the presence of heavier obscuration. The 54-month Swift BAT map shows excess hard X-ray emission likely related to a nearby (z=0.009) Type 2 AGN, close enough to IRAS 09104+4109 to significantly enhance and contaminate its emission in the early BeppoSAX PDS data.
