The XMM deep survey in the CDF-S Vignali, C; Iwasawa, K; Comastri, A ...
Astronomy and astrophysics (Berlin),
11/2015, Letnik:
583
Journal Article
Recenzirano
In active galactic nuclei (AGN)-galaxy co-evolution models, AGN winds and outflows are often invoked to explain why super-massive black holes and galaxies stop growing efficiently at a certain phase ...of their lives. They are commonly referred to as the leading actors of feedback processes. Evidence of ultra-fast (v > ~ 0.05c) outflows in the innermost regions of AGN has been collected in the past decade by sensitive X-ray observations for sizable samples of AGN, mostly at low redshift. Here we present ultra-deep XMM-Newton and Chandra spectral data of an obscured (N sub(H) asymptotically = 2 x 10 super(23) cm super(-2)), intrinsically luminous (L sub(2-10 keV) asymptotically = 4 x 10 super(44) erg s super(-1)) quasar (named PID352) at z asymptotically = 1.6 (derived from the X-ray spectral analysis) in the Chandra Deep Field-South. The source is characterized by an iron emission and absorption line complex at observed energies of E asymptotically = 2-3 keV. While the emission line is interpreted as being due to neutral iron (consistent with the presence of cold absorption), the absorption feature is due to highly ionized iron transitions (FeXXV, FeXXVI) with an outflowing velocity of 0.14 super(+0.02) sub(-0.06)c, as derived from photoionization models. The mass outflow rate - ~2 M sub(middot in circle) yr super(-1) - is similar to the source accretion rate, and the derived mechanical energy rate is ~9.5 x 10 super(44) erg s super(-1), corresponding to 9% of the source bolometric luminosity. PID352 represents one of the few cases where indications of X-ray outflowing gas have been observed at high redshift thus far. This wind is powerful enough to provide feedback on the host galaxy.
We publicly release the spectroscopic and photometric redshift catalog of the sources detected with
Chandra
in the field of the
z
= 6.3 quasar SDSS J1030+0525. This is currently the fifth-deepest ...extragalactic X-ray field, and reaches a 0.5–2 keV flux limit of
f
0.5 − 2
= 6 × 10
−17
erg s
−1
cm
−2
. Using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which come from an INAF-Large Binocular Telescope (LBT) Strategic Program. We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it to be in agreement with that of other X-ray surveys which used a similar number of photometric data points. In particular, we measure a sample normalized median absolute deviation of
σ
NMAD
= 1.48 × median(||
z
phot
−
z
spec
||/(1 +
z
spec
)) = 0.065. We use these new spectroscopic and photometric redshifts to study the properties of the
Chandra
J1030 field. We observe several peaks in our spectroscopic redshift distribution between
z
= 0.15 and
z
= 1.5, and find that the sources in each peak are often distributed across the whole
Chandra
field of view. This confirms that X-ray-selected AGNs can efficiently track large-scale structures over physical scales of several megaparsecs. Finally, we computed the
Chandra
J1030
z
> 3 number counts: while the spectroscopic completeness of our sample is limited at high redshift, our results point towards a potential source excess at
z
≥ 4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns.
Highly obscured active galactic nuclei (AGN) are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black ...hole accretion rate density. Furthermore, Compton-thick (CT) absorbers (NH ≳ 1024 cm-2) suppress even the hard X-ray (2−10 keV) AGN nuclear emission, and therefore the column density distribution above 1024 cm-2 is largely unknown. We present the identification and multi-wavelength properties of a heavily obscured (NH ≳ 1025 cm-2), intrinsically luminous (L2−10 > 1044 erg s-1) AGN at z = 0.353 in the COSMOS field. Several independent indicators, such as the shape of the X-ray spectrum, the decomposition of the spectral energy distribution and X-ray/NeV and X-ray/6 μm luminosity ratios, agree on the fact that the nuclear emission must be suppressed by a ≳1025 cm-2 column density. The host galaxy properties show that this highly obscured AGN is hosted in a massive star-forming galaxy, showing a barred morphology, which is known to correlate with the presence of CT absorbers. Finally, asymmetric and blueshifted components in several optical high-ionization emission lines indicate the presence of a galactic outflow, possibly driven by the intense AGN activity (LBol/LEdd = 0.3−0.5). Such highly obscured, highly accreting AGN are intrinsically very rare at low redshift, whereas they are expected to be much more common at the peak of the star formation and BH accretion history, at z ~ 2−3. We demonstrate that a fully multi-wavelength approach can recover a sizable sample of such peculiar sources in large and deep surveys such as COSMOS.
We probe the emission mechanism of the accreting super massive black holes in the high redshift Universe and, to do this, we study the X-ray spectrum of ULAS1120+064, the highest redshift quasar ...detected so far at z = 7.085, which has been deeply observed (340 ks) by XMM-Newton. Despite the long integration time, the spectral analysis is limited by the poor statistics, with only 150 source counts being detected. We measured the spectrum in the 2−80 keV rest-frame (0.3−10 keV observed) energy band. Assuming a simple power law model, we find a photon index of 2.0 ± 0.3 and a luminosity of 6.7 ± 0.3 × 1044 erg s-1 in the 2−10 keV band, while the intrinsic absorbing column can only be loosely constrained (NH < 1023 cm-2). Combining our measure with published data, we calculate that the X-ray-to-optical spectral index αOX is 1.8 ± 0.1, in agreement with the αOX-UV luminosity correlation that is valid for lower redshift quasars. This is the second time that a z > 6 quasar has been investigated through a deep X-ray observation. In agreement with previous studies of z ~ 6 AGN samples, we do not find any hint of evolution in the broadband energy distribution. Indeed from our dataset, ULAS 1120+0641 is indistinguishable from the population of optically bright quasar at lower redshift.
We present new and archival Chandra snapshot (≈10 ks each) observations of 15 optically identified from the Sloan Digital Sky Survey (SDSS) Type 2 quasars at z= 0.40–0.73. When combined with existing ...X-ray data, this work provides complete X-ray coverage for all 25 radio-quiet Type 2 quasars with log LO III > 9.28 L⊙ from Zakamska et al. Two targets out of 15 were not detected by Chandra and most of the remaining sources are X-ray weak, with nine having less than 10 counts in the 0.5–8 keV band. Low- to moderate-quality spectral analysis was limited to three sources, whose properties are consistent with the presence of column densities in the range NH≈ 1022–1023 cm−2 in the source rest frame. If the O iii luminosity is a reliable proxy for the intrinsic X-ray luminosity, the current X-ray data indicate that Compton-thick quasars may hide among ≈65 per cent of the SDSS Type 2 quasar population (LX,meas/LX,O III < 0.01); however, since the Type 2 quasar sample is selected on O iii luminosity, the estimated Compton-thick quasar fraction may be overestimated. Using archival Spitzer observations, we find that ≈50 per cent of SDSS Type 2 quasars appear to be obscured by Compton-thick material based on both the LX,meas/LX,mid-IR (where mid-IR corresponds to rest frame 12.3 μm) and LX,meas/LX,O III ratios. We use this information to provide an estimate of the Compton-thick quasar number density at z≈ 0.3–0.8, which we find is in broad agreement with the expectations from X-ray background models.
We present point-source catalogs for the sim2 Ms exposure of the Chandra Deep Field-South (CDF-S); this is one of the two most sensitive X-ray surveys ever performed. The survey covers an area of ...sim436 arcmin super(2) and reaches on-axis sensitivity limits of simimage and simimage ergs cm super(-2) s super(-1) for the 0.5-2.0 and 2-8 keV bands, respectively. Four hundred and sixty-two X-ray point sources are detected in at least one of three X-ray bands that were searched; 135 of these sources are new compared to the previous sim1 Ms CDF-S detections. Source positions are determined using centroid and matched-filter techniques; the median positional uncertainty is sim0.36 super(image ). The X-ray-to-optical flux ratios of the newly detected sources indicate a variety of source types; sim55% of them appear to be active galactic nuclei, while sim45% appear to be starburst and normal galaxies. In addition to the main Chandra catalog, we provide a supplementary catalog of 86 X-ray sources in the sim2 Ms CDF-S footprint that was created by merging the sim250 ks Extended Chandra Deep Field-South with the CDF-S; this approach provides additional sensitivity in the outer portions of the CDF-S. A second supplementary catalog that contains 30 X-ray sources was constructed by matching lower significance X-ray sources to bright optical counterparts; the majority of these sources appear to be starburst and normal galaxies. The total number of sources in the main and supplementary catalogs is 578. Optical R-band counterparts and basic optical and infrared photometry are provided for the X-ray sources in the main and supplementary catalogs. We also include existing spectroscopic redshifts for 224 of the X-ray sources. The average backgrounds in the 0.5-2.0 and 2-8 keV bands are 0.066 and 0.167 counts Ms super(-1) pixel super(-1), respectively, and the background counts follow Poisson distributions. The effective exposure times and sensitivity limits of the CDF-S are now comparable to those of the sim2 Ms Chandra Deep Field-North (CDF-N). We also present cumulative number counts for the main catalog and compare the results to those for the CDF-N. The soft-band number counts for these two fields agree well with each other at fluxes higher than simimage ergs cm super(-2) s super(-1), while the CDF-S number counts are up to sim25% smaller than those for the CDF-N at fluxes below simimage ergs cm super(-2) s super(-1) in the soft band and simimage ergs cm super(-2) s super(-1) in the hard band, suggesting small field-to-field variations.
We present the results of a program to acquire high-quality optical spectra of X-ray sources detected in the Extended-Chandra Deep Field-South (E-CDF-S) and its central 2 Ms area. New spectroscopic ...redshifts, up to z = 4, are measured for 283 counterparts to Chandra sources with deep exposures (t ~ 2-9 hr per pointing) using multi-slit facilities on both VLT (VIMOS) and Keck (DEIMOS), thus bringing the total number of spectroscopically identified X-ray sources to over 500 in this survey field. Since our new spectroscopic identifications are mainly associated with X-ray sources in the shallower 250 ks coverage, we provide a comprehensive catalog of X-ray sources detected in the E-CDF-S including the optical and near-infrared counterparts, determined by a likelihood routine, and redshifts (both spectroscopic and photometric), that incorporate published spectroscopic catalogs, thus resulting in a final sample with a high fraction (80%) of X-ray sources having secure identifications. We demonstrate the remarkable coverage of the luminosity-redshift plane now accessible from our data while emphasizing the detection of active galactic nuclei (AGNs) that contribute to the faint end of the luminosity function (L 0.5-8 keV ~ 1043-1044 erg s--1) at 1.5 z 3 including those with and without broad emission lines. Our redshift catalog includes 17 type-2 QSOs at 1 z 3.5 that significantly increases such samples (2X). Based on our deepest (9 hr) VLT/VIMOS observation, we identify 'elusive' optically faint galaxies (R mag ~ 25) at z ~ 2-3 based upon the detection of interstellar absorption lines (e.g., O II+Si IV, C II, C IV); we highlight one such case, an absorption-line galaxy at z = 3.208 having no obvious signs of an AGN in its optical spectrum. In addition, we determine accurate distances to eight galaxy groups with extended X-ray emission detected both by Chandra and XMM-Newton. Finally, we measure the physical extent of known large-scale structures (z ~ 0.7) evident in the CDF-S. While a thick sheet (a radial size of 67.7 Mpc) at z ~ 0.67 extends over the full field, the z ~ 0.73 structure is thin (18.8 Mpc) and filamentary as traced by both AGNs and galaxy groups. In the Appendix, we provide spectroscopic redshifts for 49 counterparts to fainter X-ray sources detected only in the 1 and 2 Ms catalogs, and 48 Very Large Array radio sources not detected in X-rays.
A large population of heavily obscured, Compton-thick active galactic nuclei (AGNs) is predicted by AGN synthesis models for the cosmic X-ray background and by the 'relic' supermassive black hole ...mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGNs. Alternative selection criteria, combining mid-infrared with near-infrared, and optical photometry, have instead been successful in pinpointing a large population of Compton-thick AGNs. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the Cosmic Evolution Survey (COSMOS) field to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density, and therefore large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24 mm fluxes higher than 550 mJy. For the MIPS sources not directly detected in the Chandra images, we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population, we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations, including both obscured AGN and star-forming galaxies. The volume density of Compton-thick QSOs (log L(2-10 keV) = 44-45 erg s-1, or loglL l(5.8 mm) = 44.79-46.18 erg s-1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) X 10-6 Mpc-3 in the redshift bin 1.2-2.2. This density is ~44% of all X-ray-selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of the most up-to-date AGN synthesis models for the cosmic X-ray background (Gilli et al. 2007). The density of lower luminosity Compton-thick AGNs (log L(2-10 keV) = 43.5-44) at z = 0.7-1.2 is (3.7 ± 1.1) X 10-5 Mpc-3, corresponding to ~67% of X-ray-selected AGNs. The comparison between the fraction of infrared-selected, Compton-thick AGNs to the X-ray selected, unobscured, and moderately obscured AGNs at high and low luminosity suggests that Compton-thick AGNs follow a luminosity dependence similar to that discovered for Compton-thin AGNs, becoming relatively rarer at high luminosities. We estimate that the fraction of AGNs (unobscured, moderately obscured, and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24 mm fluxes. We discuss how our findings can constrain AGN feedback models.
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