We investigate the possibility of using the ratio between the 2–10 keV flux and the Ne V3426 emission line flux (X/NeV) as a diagnostic diagram to discover heavily obscured, possibly Compton-thick ...active galactic nuclei (AGN) in the distant Universe. While it is on average about one order of magnitude fainter than the more commonly used O III5007 emission line, the Ne V3426 line can be observed with optical spectroscopy up to z~1.5, whereas the O III5007 line is redshifted out of the optical bands already at z~0.8. First, we calibrated a relation between X/NeV and the cold absorbing column density NH using a sample of 74 bright, nearby Seyferts with both X-ray and Ne V data available in the literature and for which the column density is determined unambiguously. Similar to what is found for the X-ray to O III5007 flux ratio (X/OIII), we found that the X/NeV ratio decreases towards high column densities, as expected if Ne V3426 emission is a good tracer of the AGN intrinsic power. Essentially all local Seyferts with X/NeV values below 15 are found to be Compton-thick objects. At X/NeV values below 100, the percentage of Compton-thick nuclei decreases to ~50%, but ~80% of the considered sample is still absorbed with NH > 1023 cm-2. Second, we applied this diagnostic diagram to different samples of distant obscured and unobscured QSOs in the Sloan Digital Sky Survey (SDSS). SDSS blue, unobscured, type-1 QSOs in the redshift range z = 0.1–1.5 indeed show X/NeV values typical of unobscured Seyfert 1s in the local Universe. Conversely, SDSS type-2 QSOs at z~0.5 classified either as Compton-thick or Compton-thin on the basis of their X/OIII ratio, would have mostly been classified in the same way based on the X/NeV ratio. We applied the X/NeV diagnostic diagram to 9 SDSS obscured QSOs in the redshift range z = 0.85–1.31, selected by means of their prominent Ne V3426 line (rest EW > 4 Å) and observed with Chandra ACIS-S for 10ks each (8 of them as part of our proprietary program). Based on the X/NeV ratio, complemented by X-ray spectral analysis, 2 objects appear good Compton-thick QSO candidates, 4 objects appear as Compton-thin QSOs, while 3 have an ambiguous classification. When excluding broad-lined QSOs with a red continuum from the sample and thus considering only genuine narrow-line objects, the efficiency in selecting Compton-thick QSOs through the Ne V line is about 50% (with large errors, though), more similar to what is achieved with O III selection. We discuss the possibility of applying the X/NeV diagnostic to deep X-ray surveys to search for Compton-thick Seyferts at z~1, i.e., those objects that are thought to be responsible for the “missing” X-ray background. Finally, we compared the optical spectral properties of Ne V-selected QSOs with those of other SDSS populations of obscured and unobscured QSOs. By restricting the analysis to objects in the same redshift (and luminosity) range z = 0.4–1.5, we found evidence that, at any given Ne V luminosity, increasing obscuration is accompanied by increasing O II3727 emission. This correlation is interpreted as evidence of enhanced star formation in obscured QSOs, which is consistent with current popular scenarios of BH-galaxy coevolution.
We present an X-ray point-source catalogue from the XMM-Large Scale Structure (XMMLSS) survey region, one of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields. We target ...the XMM-LSS region with 1.3 Ms of new XMM-Newton AO-15 observations, transforming the archival X-ray coverage in this region into a 5.3 deg2 contiguous field with uniform X-ray coverage totaling 2.7 Ms of flare-filtered exposure, with a 46 ks median PN exposure time. We provide an X-ray catalogue of 5242 sources detected in the soft (0.5-2 keV), hard (2-10 keV), and/or full (0.5-10 keV) bands with a 1 per cent expected spurious fraction determined from simulations. A total of 2381 new X-ray sources are detected compared to previous source catalogues in the same area. Our survey has flux limits of 1.7 × 10-15, 1.3 × 10-14, and 6.5 × 10-15 erg cm-2 s-1 over 90 per cent of its area in the soft, hard, and full bands, respectively, which is comparable to those of the XMM-COSMOS survey. We identify multiwavelength counterpart candidates for 99.9 per cent of the X-ray sources, of which 93 per cent are considered as reliable based on their matching likelihood ratios. The reliabilities of these high-likelihood-ratio counterparts are further confirmed to be ≈97 per cent reliable based on deep Chandra coverage over ≈5 per cent of the XMM-LSS region. Results of multiwavelength identifications are also included in the source catalogue, along with basic optical-to-infrared photometry and spectroscopic redshifts from publicly available surveys. We compute photometric redshifts for X-ray sources in 4.5 deg2 of our field where forced-aperture multiband photometry is available; > 70 per cent of the X-ray sources in this subfield have either spectroscopic or high-quality photometric redshifts.
ABSTRACT
Active galactic nuclei (AGNs) feedback has a major impact on to the supermassive black hole (SMBH) growth, the properties of the host galaxies, and their cosmic evolution. We investigate the ...effects of different kinetic feedback prescriptions on the observable properties of AGN and their host galaxies at z > 6 in a suite of zoom-in cosmological simulations. We find that kinetic feedback decreases the column density of the interstellar medium (ISM) in the host galaxy by up to a factor of ≈10, especially when the SMBHs reach high accretion rates ($\approx 10{-}30\, \mathrm{M_\odot \, yr^{-1}}$). In particular, kinetic feedback is required to extend the ISM size to >1 kpc and match the observed sizes of the gas reservoirs in z > 6 AGN host galaxies. Moreover, it produces unobscured lines of sight along which the AGN can be detected in the rest-frame UV band with magnitudes consistent with observed values of z > 6 AGN. The assumed geometry of the outflow plays an important role in shaping the observed properties of high-redshift AGN. We find that a biconical geometry is favoured over a spherical one to reproduce the observed properties, but it overestimates the number of multiple AGN systems detectable in X-ray observations. This result suggests that simplistic BH seeding recipes widely employed in cosmological simulations produce too many X-ray detectable multiple AGN at z = 6−7, thus soliciting the adoption of more physically motivated seeding prescriptions.
ABSTRACT We present the measurement of the projected and redshift-space two-point correlation function (2pcf) of the new catalog of Chandra COSMOS-Legacy active galactic nucleus (AGN) at 2.9 ≤ z ≤ ...5.5 ( 〈 L bol 〉 ∼ 1046 erg s−1) using the generalized clustering estimator based on phot-z probability distribution functions in addition to any available spec-z. We model the projected 2pcf, estimated using πmax = 200 h−1 Mpc with the two-halo term and we derive a bias at z ∼ 3.4 equal to b = 6.6 − 0.55 + 0.60 , which corresponds to a typical mass of the hosting halos of log Mh = 12.83 − 0.11 + 0.12 h−1 M . A similar bias is derived using the redshift-space 2pcf, modeled including the typical phot-z error z = 0.052 of our sample at z ≥ 2.9. Once we integrate the projected 2pcf up to πmax = 200 h−1 Mpc, the bias of XMM and Chandra COSMOS at z = 2.8 used in Allevato et al. is consistent with our results at higher redshifts. The results suggest only a slight increase of the bias factor of COSMOS AGNs at z 3 with the typical hosting halo mass of moderate-luminosity AGNs almost constant with redshift and equal to log Mh = 12.92 − 0.18 + 0.13 at z = 2.8 and log Mh = 12.83 − 0.11 + 0.12 at z ∼ 3.4, respectively. The observed redshift evolution of the bias of COSMOS AGNs implies that moderate-luminosity AGNs still inhabit group-sized halos at z 3, but slightly less massive than observed in different independent studies using X-ray AGNs at z ≤ 2.
Context.
In their evolution, star-forming galaxies are known to follow scaling relations between some fundamental physical quantities, such as the relation between mass metallicity and star formation ...main sequence.
Aims.
We study the evolution of galaxies that at a given redshift, lie simultaneously on the mass-metallicity and main-sequence relations (MZR, MSR).
Methods.
To this aim, we used the analytical leaky-box chemical evolution model, in which galaxy evolution is described by the infall timescale
τ
and the wind efficiency
λ
. We provide a detailed analysis of the temporal evolution of their metallicity, stellar mass, mass-weighted age, and gas fraction.
Results.
The evolution of the galaxies lying on the MZR and MSR at
z
∼ 0.1 suggests that the average infall timescale in two different bins of stellar masses (
M
⋆
< 10
10
M
⊙
and
M
⋆
> 10
10
M
⊙
) decreases with decreasing redshift through the addition of new galaxies with shorter timescales. This means that at each redshift, only the youngest galaxies can be assembled on the shortest timescales and still belong to the star-forming MSR. In the lowest mass bin, a decrease in median
τ
is accompanied by an increase in the median
λ
value. This implies that systems that formed at more recent times will need to eject a larger amount of mass to retain their low metallicity values. Another important result is that galactic downsizing, as traced by the age-mass relation, is naturally recovered by imposing the local MZR and MSR for star-forming galaxies. This result is retained even when a constant star formation efficiency for different galactic masses is assumed (without imposing the observed scaling relation between stellar mass and gas-depletion time-scales). Finally, we study the evolution of the hosts of C
IV
-selected active galactic nuclei, which at
z
∼ 2 follow a flat MZR. When we impose that these systems lie on the MSR, we find an “inverted” MZR at lower redshifts, meaning that some additional processes must be at play in their evolution.
Conclusions.
In our model, galactic downsizing is a direct consequence of the MZR and MSR for star-forming galaxies. This poses a challenge for models of galaxy evolution within a cosmological framework.
Abstract
We investigate the extreme X-ray variability of a
z
= 1.608 active galactic nucleus in the 7 Ms Chandra Deep Field-South (XID 403), which showed two significant X-ray brightening events. In ...the first event, XID 403 brightened by a factor of >2.5 in ≲6.1 rest-frame days in the observed-frame 0.5–5 keV band. The event lasted for ≈5.0–7.3 days, and then XID 403 dimmed by a factor of >6.0 in ≲6.1 days. After ≈1.1–2.5 yr in the rest frame (including long observational gaps), it brightened again, with the 0.5–5 keV flux increasing by a factor of >12.6. The second event lasted over 251 days, and the source remained bright until the end of the 7 Ms exposure. The spectrum is a steep power law (photon index Γ = 2.8 ± 0.3) without obscuration during the second outburst, and the rest-frame 2–10 keV luminosity reaches
1.5
−
0.5
+
0.8
×
10
43
erg
s
−
1
; there is no significant spectral evolution within this epoch. The infrared-to-UV spectral energy distribution of XID 403 is dominated by the host galaxy. There is no significant optical/UV variability and
R
-band (rest-frame ≈2500 Å) brightening contemporaneous with the X-ray brightening. The extreme X-ray variability is likely due to two X-ray unveiling events, where the line of sight to the corona is no longer shielded by high-density gas clumps in a small-scale dust-free absorber. XID 403 is probably a high-redshift analog of local narrow-line Seyfert 1 galaxies, and the X-ray absorber is a powerful accretion disk wind. On the other hand, we cannot exclude the possibility that XID 403 is an unusual candidate for tidal disruption events.
We present source catalogs for the 4 Ms Chandra Deep Field-South (CDF-S), which is the deepest Chandra survey to date and covers an area of 464.5 arcmin2. We provide a main Chandra source catalog, ...which contains 740 X-ray sources that are detected with WAVDETECT at a false-positive probability threshold of 10--5 in at least one of three X-ray bands (0.5-8 keV, full band; 0.5-2 keV, soft band; and 2-8 keV, hard band) and also satisfy a binomial-probability source-selection criterion of P < 0.004 (i.e., the probability of sources not being real is less than 0.004); this approach is designed to maximize the number of reliable sources detected. A total of 300 main-catalog sources are new compared to the previous 2 Ms CDF-S main-catalog sources. We determine X-ray source positions using centroid and matched-filter techniques and obtain a median positional uncertainty of 042. We also provide a supplementary catalog, which consists of 36 sources that are detected with WAVDETECT at a false-positive probability threshold of 10--5, satisfy the condition of 0.004 < P < 0.1, and have an optical counterpart with R < 24. Multiwavelength identifications, basic optical/infrared/radio photometry, and spectroscopic/photometric redshifts are provided for the X-ray sources in the main and supplementary catalogs. Seven hundred sixteen (97%) of the 740 main-catalog sources have multiwavelength counterparts, with 673 (94% of 716) having either spectroscopic or photometric redshifts. The 740 main-catalog sources span broad ranges of full-band flux and 0.5-8 keV luminosity; the 300 new main-catalog sources span similar ranges although they tend to be systematically lower. Basic analyses of the X-ray and multiwavelength properties of the sources indicate that >75% of the main-catalog sources are active galactic nuclei (AGNs); of the 300 new main-catalog sources, about 35% are likely normal and starburst galaxies, reflecting the rise of normal and starburst galaxies at the very faint flux levels uniquely accessible to the 4 Ms CDF-S. Near the center of the 4 Ms CDF-S (i.e., within an off-axis angle of 3'), the observed AGN and galaxy source densities have reached 9800+1300 -- 1100 deg--2 and 6900+1100 -- 900 deg--2, respectively. Simulations show that our main catalog is highly reliable and is reasonably complete. The mean backgrounds (corrected for vignetting and exposure-time variations) are 0.063 and 0.178 counts Ms--1 pixel--1 (for a pixel size of 0492) for the soft and hard bands, respectively; the majority of the pixels have zero background counts. The 4 Ms CDF-S reaches on-axis flux limits of 3.2 X 10--17, 9.1 X 10--18, and 5.5 X 10--17 erg cm--2 s--1 for the full, soft, and hard bands, respectively. An increase in the CDF-S exposure time by a factor of 2-2.5 would provide further significant gains and probe key unexplored discovery space.
We report ALMA Cycle 0 observations at 1.3 mm of LESS J033229.4-275619 (XID403), an ultraluminous infrared galaxy at z = 4.75 in the Chandra Deep Field South hosting a Compton-thick QSO. The source ...is not resolved in our data at a resolution of ~0.75 arcsec, placing an upper-limit of 2.5 kpc to the half-light radius of the continuum emission from heated-dust. After deconvolving for the beam size, however, we found a ~3σ indication of an intrinsic source size of 0.27 ± 0.08 arcsec (Gaussian FWHM), which would correspond to rhalf ~ 0.9 ± 0.3 kpc. We build the far-infrared SED of XID403 by combining datapoints from both ALMA and Herschel and fit it with a modified blackbody spectrum. For the first time, we measure the dust temperature Td = 58.5 ± 5.3 K in this system, which is comparable to what has been observed in other high-z submillimeter galaxies. The measured star formation rate is SFR = 1020 ± 150 M⊙ yr-1, in agreement with previous estimates at lower S/N. Based on the measured SFR and source size, we constrain the SFR surface density to be ΣSFR > 26M⊙ yr-1 kpc-2 (~200M⊙ yr-1 kpc-2 for rhalf ~ 0.9 kpc). The compactness of this starburst is comparable to what has been observed in other local and high-z starburst galaxies. If the gas mass measured from previous CII and CO(2–1) observations at low resolution is confined within the same dust region, assuming rhalf ~ 0.9 ± 0.3 kpc, this would produce a column density of NH ~ 0.3−1.1 × 1024 cm-2 towards the central SMBH, similar to the column density of ≈1.4 × 1024 cm-2 measured from the X-rays. Then, in principle, if both gas and dust were confined on sub-kpc scales, this would be sufficient to produce the observed X-ray column density without any need of a pc-scale absorber (e.g. the torus postulated by Unified Models). We speculate that the high compactness of star formation, together with the presence of a powerful AGN, likely produce an outflowing wind. This would be consistent with the ~350 km s-1 velocity shift observed between the Lyα emission and the submm lines (CII, CO(2–1), NII) and with the highly-ionized Fe emission line at ~6.9 keV rest-frame tentatively observed in the X-ray spectrum. Finally, our observations show that, besides the mass, star formation rate and gas depletion timescale, XID403 has also the right size to be one of the progenitors of the compact quiescent massive galaxies seen at z ~ 3.
Abstract
We present the 78 ks Chandra observations of the z = 6.4 quasar SDSS J1148+5251. The source is clearly detected in the energy range 0.3–7 keV with 42 counts (with a significance ≳9σ). The ...X-ray spectrum is best fitted by a power law with photon index Γ = 1.9 absorbed by a gas column density of
${\rm N}_{\rm H}=2.0^{+2.0}_{-1.5}\times {10}^{23}\,{\rm cm}^{-2}$
. We measure an intrinsic luminosity at 2–10 and 10–40 keV equal to ∼ 1.5 × 1045 erg s− 1, comparable with luminous local and intermediate-redshift quasar properties. Moreover, the X-ray to optical power-law slope value (αOX = −1.76 ± 0.14) of J1148 is consistent with the one found in quasars with similar rest-frame 2500 Å luminosity (L
2500 ∼ 1032 erg s
− 1 Å− 1). Then we use Chandra data to test a physically motivated model that computes the intrinsic X-ray flux emitted by a quasar starting from the properties of the powering black hole and assuming that X-ray emission is attenuated by intervening, metal-rich (Z ≥ Z⊙) molecular clouds (MC) distributed on ∼kpc scales in the host galaxy. Our analysis favours a black hole mass M
BH ∼ 3 × 109 M⊙ and a molecular hydrogen mass
$M_{\rm H_2}\sim 2\times {10}^{10}\ {\rm M_{\odot }}$
, in good agreement with estimates obtained from previous studies. We finally discuss strengths and limits of our analysis.
![The X-ray to [Ne V]3426 flu...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "The X-ray to [Ne V]3426 flux ratio: discovering heavily obscured AGN in the distant Universe")
PDF
