We report on the spectroscopic confirmation of a large-scale structure around the luminous
z
= 6.31 quasi-stellar object (QSO) SDSS J1030+0524, powered by a one billion solar mass black hole. The ...structure is populated by at least six members, namely, four Lyman-break galaxies (LBGs), and two Lyman alpha emitters (LAEs). The four LBGs were identified among a sample of 21
i
-band dropouts with
z
AB
< 25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts were determined through multi-object spectroscopic observations at 8−10 m class telescopes lasting up to eight hours. The two LAEs were identified in a 6 h VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range between 6.129−6.355. Assuming that the peculiar velocities are negligible, this range corresponds to radial separations of ±5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at a level > 3.5
σ
and that the level of the galaxy overdensity is at least 1.5−2 within the large volume sampled (∼780 physical Mpc
3
). The spectral properties of the six member galaxies (Ly
α
strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>10
12
M
⊙
) dark matter halos in large-scale structures and that the absence of earlier detections of such systems is likely due to observational limitations.
Using Chandra observations in the 2.15 deg2 COSMOS-legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the 0.3-7 keV energy band. ...The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT ∼ 0.27 and 0.07 keV and an extragalactic power law with a photon spectral index Γ = 1.45 0.02. The 1 keV normalization of the extragalactic component is 10.91 0.16 keV cm−2 s−1 sr−1 keV−1. Removing all X-ray-detected sources, the remaining unresolved CXB is best fit by a power law with normalization 4.18 0.26 keV cm−2 s−1 sr−1 keV−1 and photon spectral index Γ = 1.57 0.10. Removing faint galaxies down to leaves a hard spectrum with and a 1 keV normalization of ∼1.37 keV cm−2 s−1 sr−1 keV−1. This means that ∼91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute ∼8%-9% of the total CXB show marginal evidence of being harder and possibly more obscured than resolved sources. Another ∼1% of the CXB can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. According to these limits, we investigate a scenario where early black holes totally account for non-source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the accreted mass density, such a population of black holes must grow in Compton-thick envelopes with 1.6 × 1025 cm−2 and form in extremely low-metallicity environments .
A new, faint population of X-ray transients Bauer, Franz E; Treister, Ezequiel; Schawinski, Kevin ...
Monthly notices of the Royal Astronomical Society,
06/2017, Letnik:
467, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
We report on the detection of a remarkable new fast high-energy transient found in the Chandra Deep Field-South, robustly associated with a faint (mR = 27.5 mag, zph ∼ 2.2) host in the ...CANDELS survey. The X-ray event is comprised of 115$^{+12}_{-11}$ net 0.3–7.0 keV counts, with a light curve characterized by an ≈100 s rise time, a peak 0.3–10 keV flux of ≈5 × 10−12 erg s−1 cm−2 and a power-law decay time slope of −1.53 ± 0.27. The average spectral slope is $\Gamma = 1.43^{+0.23}_{-0.13}$, with no clear spectral variations. The X-ray and multiwavelength properties effectively rule out the vast majority of previously observed high-energy transients. A few theoretical possibilities remain: an ‘orphan’ X-ray afterglow from an off-axis short-duration gamma-ray burst (GRB) with weak optical emission, a low-luminosity GRB at high redshift with no prompt emission below ∼20 keV rest frame, or a highly beamed tidal disruption event (TDE) involving an intermediate-mass black hole and a white dwarf with little variability. However, none of the above scenarios can completely explain all observed properties. Although large uncertainties exist, the implied rate of such events is comparable to those of orphan and low-luminosity GRBs as well as rare TDEs, implying the discovery of an untapped regime for a known transient class, or a new type of variable phenomena whose nature remains to be determined.
By using a large, highly obscured ( ) active galactic nucleus (AGN) sample (294 sources at z ∼ 0-5) selected from detailed X-ray spectral analyses in the deepest Chandra surveys, we explore ...distributions of these X-ray sources in various optical/infrared/X-ray color-color diagrams and their host-galaxy properties, aiming at characterizing the nuclear obscuration environment and the triggering mechanism of highly obscured AGNs. We find that the refined Infrared Array Camera (IRAC) color-color diagram fails to identify the majority of X-ray-selected, highly obscured AGNs, even for the most luminous sources with . Over 80% of our sources will not be selected as heavily obscured candidates using the flux ratio of and R − K > 4.5 criteria, implying complex origins and conditions for the obscuring materials that are responsible for the heavy X-ray obscuration. The average star formation rate (SFR) of highly obscured AGNs is similar to that of stellar mass- (M*-) and z-controlled normal galaxies, while a lack of quiescent hosts is observed for the former. Partial correlation analyses imply that highly obscured AGN activity (traced by ) appears to be more fundamentally related to M*, and no dependence of on either M* or SFR is detected. Morphology analyses reveal that 61% of our sources have a significant disk component, while only ∼27% of them exhibit irregular morphological signatures. These findings together point toward a scenario where secular processes (e.g., galactic-disk instabilities), instead of mergers, are most probable to be the leading mechanism that triggers accretion activities of X-ray-selected, highly obscured AGNs.
ABSTRACT We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3 deg2 of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, ...6181 unique X-ray sources are significantly detected with XMM-Newton (>5 ) and Chandra (>4.5 ). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7 × 10−16 erg s−1 cm−2, 4.7 × 10−15 erg s−1 cm−2, and 2.1 × 10−15 erg s−1 cm−2 in the soft (0.5-2 keV), hard (2-10 keV), and full bands (0.5-10 keV), respectively, with approximate half-area survey flux limits of 5.4 × 10−15 erg s−1 cm−2, 2.9 × 10−14 erg s−1 cm−2, and 1.7 × 10−14 erg s−1 cm−2. We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ∼30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live.
We have analysed the XMM-Newton and Chandra data overlapping ~16.5 deg... of Sloan Digital Sky Survey Stripe 82, including ~4.6 deg2 of proprietary XMM-Newton data that we present here. In total, ...3362 unique X-ray sources are detected at high significance. We derive the XMM-Newton number counts and compare them with our previously reported Chandra logN-logS relations and other X-ray surveys. The Stripe 82 X-ray source lists have been matched to multiwavelength catalogues using a maximum likelihood estimator algorithm. We discovered the highest redshift (z = 5.86) quasar yet identified in an X-ray survey. We find 2.5 times more high-luminosity (...) AGN than the smaller area Chandra and XMM-Newton survey of COSMOS and 1.3 times as many identified by XBo...tes. Comparing the high-luminosity active galactic nuclei (AGN) we have identified with those predicted by population synthesis models, our results suggest that this AGN population is a more important component of cosmic black hole growth than previously appreciated. Approximately a third of the X-ray sources not detected in the optical are identified in the infrared, making them candidates for the elusive population of obscured high-luminosity AGN in the early universe. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT Capitalizing on the all-sky coverage of WISE and the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of mR (optical) - ...(mid-infrared), hereafter , as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ∼16.5 deg2 Stripe 82 X-ray survey data as a test bed to compare with R − K, an oft-used obscured active galactic nucleus (AGN) selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R − K versus space. We demonstrate that optically normal galaxies hosting X-ray AGNs at redshifts can be recovered with an color cut, while they typically are not selected as AGNs based on their colors. Additionally, different observed X-ray luminosity bins favor different regions in parameter space: moderate-luminosity AGNs (1043 erg erg s−1) tend to have red colors, while the highest-luminosity AGNs ( erg s−1) have bluer colors; higher spectroscopic completeness of the Stripe 82X sample is needed to determine whether this is a selection effect or an intrinsic property. Finally, we parameterize X-ray obscuration of Stripe 82X AGNs by calculating their hardness ratios (HRs) and find no clear trends between HR and optical reddening. Our results will help inform best-effort practices in following up obscured AGN candidates in current and future wide-area, shallow X-ray surveys, including the all-sky eROSITA mission.
The mid-infrared-to-ultraviolet (0.1–10 μm) spectral energy distribution (SED) shapes of 407 X-ray-selected radio-quiet type 1 active galactic nuclei (AGN) in the wide-field ‘Cosmic Evolution Survey’ ...(COSMOS) have been studied for signs of evolution. For a sub-sample of 200 radio-quiet quasars with black hole mass estimates and host galaxy corrections, we studied their mean SEDs as a function of a broad range of redshift, bolometric luminosity, black hole mass and Eddington ratio, and compared them with the Elvis et al. (E94) type 1 AGN mean SED. We found that the mean SEDs in each bin are closely similar to each other, showing no statistical significant evidence of dependence on any of the analysed parameters. We also measured the SED dispersion as a function of these four parameters, and found no significant dependences. The dispersion of the XMM-COSMOS SEDs is generally larger than E94 SED dispersion in the ultraviolet, which might be due to the broader ‘window function’ for COSMOS quasars, and their X-ray-based selection.
We report on an accurate measurement of the CXB in the 15-50 keV range performed with the Phoswich Detection System (PDS) instrument aboard the BeppoSAX satellite. We establish that the most likely ...CXB intensity level at its emission peak (26-28 keV) is approximately 40 keV cm super(-2) s super(-1) sr super(-1), a value consistent with that derived from the best available CXB measurement obtained over 25 years ago with the first High Energy Astronomical Observatory (HEAO-1) satellite mission (Gruber et al.), whose intensity, lying well below the extrapolation of some lower energy measurements performed with focusing telescopes, was questioned in recent years. We find that 90% of the acceptable solutions of our best-fit model to the PDS data give a 20-50 keV CXB flux lower than 6.5 x 10 super(-8) ergs cm super(-2) s super(-1) sr super(-1), which is 12% higher than that quoted by Gruber et al. when we use our best calibration scale. In combination with the CXB synthesis models we infer that about 25% of the intensity at similar to 30 keV arises from extremely obscured, Compton-thick AGNs (absorbing column density N sub(H) > 10 super(24) cm super(-2)), while a much larger population would be implied by the highest intensity estimates. We also infer a mass density of supermassive black holes of similar to 3 x 10 super(5) M unk Mpc super(-3). The summed contribution of resolved sources (Moretti et al.) in the 2-10 keV band exceeds our best-fit CXB intensity extrapolated to lower energies, but it is within our upper limit, so that any significant contribution to the CXB from sources other than AGNs, such as star-forming galaxies and diffuse warm-hot intergalactic medium (WHIM), is expected to be mainly confined below a few keV.
We report a sizable class of type 1 active galactic nuclei (AGNs) with unusually weak near-infrared (1-3 Delta *mm) emission in the XMM-COSMOS type 1 AGN sample. The fraction of these 'hot-dust-poor' ...AGNs increases with redshift from 6% at low redshift (z < 2) to 20% at moderate high redshift (2 < z < 3.5). There is no clear trend of the fraction with other parameters: bolometric luminosity, Eddington ratio, black hole mass, and X-ray luminosity. The 3 Delta *mm emission relative to the 1 Delta *mm emission is a factor of 2-4 smaller than the typical Elvis et al. AGN spectral energy distribution (SED), which indicates a 'torus' covering factor of 2%-29%, a factor of 3-40 smaller than required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of the source SEDs. We estimate the outer edge of their accretion disks to lie at (0.3-2.0) X 104 Schwarzschild radii, ~10-23 times the gravitational stability radii. Formation scenarios for these sources are discussed.
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