State-of-the-art models of massive black hole formation postulate that quasars at z > 6 reside in extreme peaks of the cosmic density structure in the early universe. Even so, direct observational ...evidence of these overdensities is elusive, especially on large scales (≫1 Mpc) as the spectroscopic follow-up of z > 6 galaxies is observationally expensive. Here we present Keck/DEIMOS optical and IRAM/NOEMA millimeter spectroscopy of a z ∼ 6 Lyman-break galaxy candidate originally discovered via broadband selection, at a projected separation of 4.65 physical Mpc (13.94 arcmin) from the luminous z = 6.308 quasar J1030+0524. This well-studied field presents the strongest indication to date of a large-scale overdensity around a z > 6 quasar. The Keck observations suggest a z ∼ 6.3 dropout identification of the galaxy. The NOEMA 1.2 mm spectrum shows a 3.5σ line that, if interpreted as C II, would place the galaxy at z = 6.318 (i.e., at a line-of-sight separation of 3.9 comoving Mpc assuming that relative proper motion is negligible). The measured C II luminosity is 3 × 108 L⊙, in line with expectations for a galaxy with a star formation rate ∼15 M⊙ yr−1, as inferred from the rest-frame UV photometry. Our combined observations place the galaxy at the same redshift as the quasar, thus strengthening the overdensity scenario for this z > 6 quasar. This pilot experiment demonstrates the power of millimeter-wavelength observations in the characterization of the environment of early quasars.
We present the results of a spectroscopic campaign with the Multi-Object Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope (LBT), aimed at obtaining a spectroscopic ...redshift for seven
Chandra
J1030 sources with a photometric redshift ≥2.7 and optical magnitude
r
AB
= 24.5 − 26.5. We obtained a spectroscopic redshift for five out of seven targets: all of them have
z
spec
≥ 2.5, thus probing the reliability of the
Chandra
J1030 photometric redshifts. The spectroscopic campaign led to the serendipitous discovery of a
z
∼ 2.78 large-scale structure (LSS) in the J1030 field: the structure contains four X-ray sources (three of which were targeted in the LBT-MODS campaign) and two non-X-ray-detected galaxies for which a VLT-MUSE spectrum was already available. We also find 26 galaxies with a photometric redshift in the range
z
phot
= 2.68 − 2.88, which we consider candidate LSS members. The X-ray members of the LSS are hosted in galaxies that are significantly more massive (log(
M
*
/
M
⊙
) = 10.0 − 11.1) than both those hosting the two MUSE-detected sources (log(
M
*
/
M
⊙
) < 10) and those belonging to the photometric sample (median stellar mass log(
M
*
/
M
⊙
) = 10.0). Both observations and simulations show that massive galaxies, and particularly objects with log(
M
*
/
M
⊙
) > 10, are among the best tracers of LSSs and filaments in the cosmic web. Consequently, our result can explain why X-ray-detected active galactic nuclei have also been shown to be efficient tracers of LSS.
Abstract
We present the X-ray point-source catalogs in two of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields, W-CDF-S (4.6 deg
2
) and ELAIS-S1 (3.2 deg
2
), aiming to ...fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large areas. The W-CDF-S and ELAIS-S1 regions were targeted with 2.3 and 1.0 Ms of XMM-Newton observations, respectively; 1.8 and 0.9 Ms exposures remain after flare filtering. The survey in W-CDF-S has a flux limit of 1.0 × 10
−14
erg cm
−2
s
−1
over 90% of its area in the 0.5–10 keV band; 4053 sources are detected in total. The survey in ELAIS-S1 has a flux limit of 1.3 × 10
−14
erg cm
−2
s
−1
over 90% of its area in the 0.5–10 keV band; 2630 sources are detected in total. Reliable optical-to-IR multiwavelength counterpart candidates are identified for ≈89% of the sources in W-CDF-S and ≈87% of the sources in ELAIS-S1. A total of 3129 sources in W-CDF-S and 1957 sources in ELAIS-S1 are classified as active galactic nuclei (AGNs). We also provide photometric redshifts for X-ray sources; ≈84% of the 3319/2001 sources in W-CDF-S/ELAIS-S1 with optical-to-near-IR forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. The completion of the XMM-Newton observations in the W-CDF-S and ELAIS-S1 fields marks the end of the XMM-SERVS survey data gathering. The ≈12,000 pointlike X-ray sources detected in the whole ≈13 deg
2
XMM-SERVS survey will benefit future large-sample AGN studies.
We constrain the ratio of black hole (BH) mass to total stellar mass of type-1 active galactic nuclei (AGNs) in the COSMOS survey at 1 < z < 2. For 10 AGNs at mean redshift z approx 1.4 with both ...Hubble Space Telescope (HST)/ACS and HST/NICMOS imaging data, we are able to compute the total stellar mass M {sub *,total}, based on rest-frame UV-to-optical host galaxy colors which constrain mass-to-light ratios. All objects have virial M {sub BH} estimates available from the COSMOS Magellan/IMACS and zCOSMOS surveys. We find within errors zero difference between the M {sub BH}-M {sub *,total} relation at z approx 1.4 and the M {sub BH}-M {sub *,bulge} relation in the local universe. Our interpretation is (1) if our objects were purely bulge-dominated, the M {sub BH}-M {sub *,bulge} relation has not evolved since z approx 1.4. However, (2) since we have evidence for substantial disk components, the bulges of massive galaxies (M {sub *,total} = 11.1 +- 0.3 or log M {sub BH} approx 8.3 +- 0.2) must have grown over the last 9 Gyr predominantly by redistribution of the disk into the bulge mass. Since all necessary stellar mass exists in galaxies at z = 1.4, no star formation or addition of external stellar material is required, but only a redistribution, e.g., induced by minor and major merging or through disk instabilities. Merging, in addition to redistributing mass in the galaxy, will add both BH and stellar/bulge mass, but does not change the overall final M {sub BH}/M {sub *,bulge} ratio. Since the overall cosmic stellar and BH mass buildup trace each other tightly over time, our scenario of bulge formation in massive galaxies is independent of any strong BH feedback and means that the mechanism coupling BH and bulge mass until the present is very indirect.
We present a broadband (~0.5-79 keV) spectral and temporal analysis of multiple NuSTAR observations combined with archival Suzaku and Chandra data of NGC 4945, the brightest extragalactic source at ...100 keV. We observe hard X-ray (> 10 keV) flux and spectral variability, with flux variations of a factor of two on timescales of 20 ks. A variable primary continuum dominates the high-energy spectrum (> 10 keV) in all states, while the reflected/scattered flux that dominates at E < 10 keV stays approximately constant. From modeling the complex reflection/transmission spectrum, we derive a Compton depth along the line of sight of tau sub(Thomson) ~ 2.9, and a global covering factor for the circumnuclear gas of ~0.15. This agrees with the constraints derived from the high-energy variability, which implies that most of the high-energy flux is transmitted rather than Compton-scattered. This demonstrates the effectiveness of spectral analysis at constraining the geometric properties of the circumnuclear gas, and validates similar methods used for analyzing the spectra of other bright, Compton-thick active galactic nuclei (AGNs). The lower limits on the e-folding energy are between 200 and 300 keV, consistent with previous BeppoSAX, Suzaku, and Swift Burst Alert Telescope observations. The accretion rate, estimated from the X-ray luminosity and assuming a bolometric correction typical of type 2 AGN, is in the range ~0.1-0.3 lambda sub(Edd) depending on the flux state. The substantial observed X-ray luminosity variability of NGC 4945 implies that large errors can arise from using single-epoch X-ray data to derive L/L sub(Edd) values for obscured AGNs.
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg2 of the COSMOS field (centered at 10 h, +02 o ) with an effective exposure of ~160 ks, and ...an outer 0.4 deg2 area with an effective exposure of ~80 ks. The limiting source detection depths are 1.9 X 10-16 erg cm-2 s-1 in the soft (0.5-2 keV) band, 7.3 X 10-16 erg cm-2 s-1 in the hard (2-10 keV) band, and 5.7 X 10-16 erg cm-2 s-1 in the full (0.5-10 keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2 X 10-5 (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (+/-12%) exposure across the inner 0.5 deg2 field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper. The full catalog is described here in detail and is available online.
We present JWST/NIRSpec integral field data of the quasar PJ308-21 at z = 6.2342. As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host ...galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the 2.87 − 5.27 μm wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality (signal-to-noise ratio ∼100 − 400 per spectral element). Based on the H β line from the broad line region, we obtain an estimate of the black hole mass M BH, H β ∼ 2.7 × 10 9 M ⊙ . This value is within a factor ≲1.5 of the H α -based black hole mass from the same spectrum ( M BH, H α ∼ 1.93 × 10 9 M ⊙ ) and is consistent with a previous estimate relying on the Mg II λ 2799 line ( M BH, MgII ∼ 2.65 × 10 9 M ⊙ ). All these M BH estimates are within the ∼0.5 dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21 λ Edd, H β ∼ 0.67 ( λ Edd, H α ∼ 0.96) is in line with the overall quasar population at z ≳ 6. The relative strengths of the O III , Fe II , and H β lines are consistent with the empirical “Eigenvector 1” correlations as observed for low redshift quasars. We find evidence for blueshifted O III λ 5007 emission with a velocity offset Δ v O III = −1922 ± 39 km s −1 from the systemic velocity and a full width at half maximum (FWHM) FWHM (O III ) = 2776 −74 +75 km s −1 . This may be the signature of outflowing gas from the nuclear region, despite the true values of Δ v O III and FWHM (O III ) likely being more uncertain due to the blending with H β and Fe II lines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.
Abstract We present a catalog of hard X-ray serendipitous sources detected in the first 80 months of observations by the Nuclear Spectroscopic Telescope Array (NuSTAR). The NuSTAR serendipitous ...survey 80 month (NSS80) catalog has an unprecedented ∼62 Ms of effective exposure time over 894 unique fields (a factor of 3 increase over the 40 month catalog, NSS40), with an areal coverage of ∼36 deg 2 , larger than all NuSTAR extragalactic surveys. NSS80 provides 1274 hard X-ray sources in the 3−24 keV band (822 new detections compared to the previous NSS40). Approximately 76% of the NuSTAR sources have lower-energy (<10 keV) X-ray counterparts from Chandra, XMM-Newton, and Swift-XRT. We have undertaken an extensive campaign of ground-based spectroscopic follow-up to obtain new source redshifts and classifications for 427 sources. Combining these with existing archival spectroscopy provides redshifts for 550 NSS80 sources, of which 547 are classified. The sample is primarily composed of active galactic nuclei (AGNs), detected over a large range in redshift ( z = 0.012–3.43), but also includes 58 spectroscopically confirmed Galactic sources. In addition, five AGN–galaxy pairs, one dual AGN system, one BL Lac candidate, and a hotspot of 4C 74.26 (radio quasar) have been identified. The median rest-frame 10−40 keV luminosity and redshift of NSS80 are 〈 L 10−40 keV 〉 = 1.2 × 10 44 erg s −1 and 〈 z 〉 = 0.56. We investigate the optical properties and construct composite optical spectra to search for subtle signatures not present in the individual spectra, finding an excess of redder BL AGNs compared to optical quasar surveys, predominantly due to the presence of the host galaxy and, at least in part, due to dust obscuration.
We present optical spectroscopy for an X-ray and optical flux-limited sample of 677 XMM-Newton selected targets covering the 2 deg2 Cosmic Evolution Survey field, with a yield of 485 high-confidence ...redshifts. The majority of the spectra were obtained over three seasons (2005-2007) with the Inamori Magellan Areal Camera and Spectrograph instrument on the Magellan (Baade) telescope. We also include in the sample previously published Sloan Digital Sky Survey spectra and supplemental observations with MMT/Hectospec. We detail the observations and classification analyses. The survey is 90% complete to flux limits of f 0.5-10 keV > 8 X 10-16 erg cm-2 s-1 and i + AB < 22, where over 90% of targets have high-confidence redshifts. Making simple corrections for incompleteness due to redshift and spectral type allows for a description of the complete population to i + AB < 23. The corrected sample includes a 57% broad emission line (Type 1, unobscured) active galactic nucleus (AGN) at 0.13 < z < 4.26, 25% narrow emission line (Type 2, obscured) AGN at 0.07 < z < 1.29, and 18% absorption line (host-dominated, obscured) AGN at 0 < z < 1.22 (excluding the stars that made up 4% of the X-ray targets). We show that the survey's limits in X-ray and optical fluxes include nearly all X-ray AGNs (defined by L 0.5-10 keV > 3 X 1042 erg s-1) to z < 1, of both optically obscured and unobscured types. We find statistically significant evidence that the obscured-to-unobscured AGN ratio at z < 1 increases with redshift and decreases with luminosity.
We present the first results of a wide-area X-ray survey within the Sloan Digital Sky Survey Stripe 82, a 300 deg2 region of the sky with a substantial investment in multiwavelength coverage. We ...analysed archival Chandra observations that cover 6.2 deg2 within Stripe 82 ('Stripe 82 ACX'), reaching 4.5σ flux limits of 1.2 × 10−15, 5.4 × 10−15 and 2.9 × 10−15 erg s−1 cm−2 in the soft (0.5-2 keV), hard (2-7 keV) and full (0.5-7 keV) bands, to find 480, 137 and 705 X-ray sources, respectively. 214 sources are detected only in the full band and 4 sources are detected solely in the soft band. Utilizing data products from the Chandra Source Catalog, we construct independent
relationships, detailing the number density of X-ray sources as a function of flux. The soft and full bands show general agreement with previous Chandra surveys; the hard band number counts agree among Stripe 82 ACX, XBoötes and XDEEP2, but all three are somewhat systematically lower than the counts derived from Chandra Multiwavelength Project. We compare the luminosity distribution of Stripe 82 ACX with the smaller, deeper Chandra
Deep Field-South, Extended Chandra Deep Field-South and Chandra-COSMOS surveys to illustrate the benefit of wide-area surveys in locating high-luminosity and/or high-redshift active galactic nuclei (AGN). Finally, we compare the identified AGN with predictions from population synthesis models, noting that prior to any spectroscopic follow-up campaign, we have already located roughly half the high-luminosity quasars at high redshift expected to lie within the survey area. However, our data also suggest that refinements to population synthesis models will be required.
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