We present X-shooter at Very Large Telescope observations of a sample of 10 luminous, X-ray obscured quasi-stellar objects (QSOs) at z ~ 1.5 from the XMM-COSMOS survey, expected to be caught in the ...transitioning phase from starburst to active galactic nucleus (AGN)-dominated systems. The main selection criterion is X-ray detection at bright fluxes (...) coupled to red optical-to-near-infrared-to-mid-infrared colours. Thanks to its large wavelength coverage, X-shooter allowed us to determine accurate redshifts from the presence of multiple emission lines for five out of six targets for which we had only a photometric redshift estimate, with an 80 per cent success rate, significantly larger than what is observed in similar programs of spectroscopic follow-up of red QSOs. We report the detection of broad and shifted components in the OIII ...5007, 4959 complexes for six out of eight sources with these lines observable in regions free from strong atmospheric absorptions. The full width at half-maximum (FWHM) associated with the broad components are in the range FWHM ~ 900-1600 km s..., larger than the average value observed in Sloan Digital Sky Survey type 2 AGN samples at similar observed OIII luminosity, but comparable to those observed for QSO/ultraluminous infrared galaxies systems for which the presence of kpc scale outflows has been revealed through integral field unit spectroscopy. Although the total outflow energetics (inferred under reasonable assumptions) may be consistent with winds accelerated by stellar processes, we favour an AGN origin for the outflows given the high outflow velocities observed (...) and the presence of strong winds also in objects undetected in the far-infrared. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We present ALMA observations at 107.291 GHz (band 3) and 214.532 GHz (band 6) of GMASS 0953, a star-forming galaxy at z = 2.226 hosting an obscured active galactic nucleus (AGN) that has ...been proposed as a progenitor of compact quiescent galaxies (QGs). We measure for the first time the size of the dust and molecular gas emission of GMASS 0953 that we find to be extremely compact (∼1 kpc). This result, coupled with a very high interstellar medium (ISM) density (n ∼ 105.5 cm−3), a low gas mass fraction (∼0.2), and a short gas depletion time-scale (∼150 Myr), implies that GMASS 0953 is experiencing an episode of intense star formation in its central region that will rapidly exhaust its gas reservoirs, likely aided by AGN-induced feedback, confirming its fate as a compact QG. Kinematic analysis of the CO(6–5) line shows evidence of rapidly rotating gas (Vrot = 320$^{+92}_{-53}$ km s−1), as observed also in a handful of similar sources at the same redshift. On-going quenching mechanisms could either destroy the rotation or leave it intact leading the galaxy to evolve into a rotating QG.
We study the incidence of nuclear obscuration on a complete sample of 1310 active galactic nuclei (AGN) selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMM-COSMOS survey, in ...the redshift range 0.3 < z < 3.5. We classify the AGN as obscured or unobscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70 per cent of the objects, and the remaining 30 per cent can be further subdivided into two distinct classes: at low luminosities X-ray unobscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at high-luminosities broad-line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and unobscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.
The estimate of stellar metallicities (
Z
*
) of high-
z
galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar ...mass, dust attenuation, stellar age, and metallicity. Benefiting from uniquely deep far-UV spectra of > 500 star-forming galaxies at redshifts 2 <
z
< 5 extracted from the VANDELS survey and stacked in bins of stellar mass (
M
*
) and UV continuum slope (
β
), we estimate their stellar metallicities
Z
*
from stellar photospheric absorption features at 1501 and 1719 Å, which are calibrated with Starburst99 models and are largely unaffected by stellar age, dust, IMF, nebular continuum, or interstellar absorption. Comparing them to photometric-based spectral slopes in the 1250–1750 Å range, we find that the stellar metallicity increases by ∼0.5 dex from
β
∼ −2 to
β
∼ −1 (1 ≲
A
1600
≲ 3.2), and a dependence with
β
holds at fixed UV absolute luminosity
M
UV
and stellar mass up to ∼10
9.65
M
⊙
. As a result, metallicity is a fundamental ingredient for properly rescaling dust corrections based on
M
UV
and
M
*
. Using the same absorption features, we analyzed the mass-metallicity relation (MZR), and find it to be consistent with the previous VANDELS estimation based on a global fit of the FUV spectra. Similarly, we do not find a significant evolution between
z
∼ 2 and
z
∼ 3.5. Finally, the slopes of our MZR and
Z
*
−
β
relation are in agreement with the predictions of well-studied semi-analytic models (SAM) of galaxy formation, while some tensions remain concerning the absolute metallicity normalization. The relation between the UV slope and stellar metallicity is fundamental to the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our Universe.
ABSTRACT
While the kinematics of galaxies up to z ∼ 3 have been characterized in detail, only a handful of galaxies at high redshift (z > 4) have been examined in such a way. The Atacama Large ...Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C ii at Early times (ALPINE) survey observed a statistically significant sample of 118 star-forming main-sequence galaxies at z = 4.4–5.9 in C ii158 $\mu$m emission, increasing the number of such observations by nearly 10×. A preliminary qualitative classification of these sources revealed a diversity of kinematic types (i.e. rotators, mergers, and dispersion-dominated systems). In this work, we supplement the initial classification by applying quantitative analyses to the ALPINE data: a tilted ring model (TRM) fitting code (3Dbarolo), a morphological classification (Gini-M20), and a set of disc identification criteria. Of the 75 C ii-detected ALPINE galaxies, 29 are detected at sufficient significance and spatial resolution to allow for TRM fitting and the derivation of morphological and kinematic parameters. These 29 sources constitute a high-mass subset of the ALPINE sample ($M_*\gt 10^{9.5}\, \mathrm{M}_{\odot }$). We robustly classify 14 of these sources (six rotators, five mergers, and three dispersion-dominated systems); the remaining sources showing complex behaviour. By exploring the G-M20 of z > 4 rest-frame far-infrared and C ii data for the first time, we find that our 1 arcsec ∼ 6 kpc resolution data alone are insufficient to separate galaxy types. We compare the rotation curves and dynamical mass profiles of the six ALPINE rotators to the two previously detected z ∼ 4–6 unlensed main-sequence rotators, finding high rotational velocities (∼50–250 km s−1) and a diversity of rotation curve shapes.
We unveil the complex shape of a proto-supercluster at z ∼ 2.45 in the COSMOS field exploiting the synergy of both spectroscopic and photometric redshifts. Thanks to the spectroscopic redshifts of ...the VIMOS Ultra-Deep Survey (VUDS), complemented by the zCOSMOS-Deep spectroscopic sample and high-quality photometric redshifts, we compute the three-dimensional (3D) overdensity field in a volume of ∼100 × 100 × 250 comoving Mpc3 in the central region of the COSMOS field, centred at z ∼ 2.45 along the line of sight. The method relies on a two-dimensional (2D) Voronoi tessellation in overlapping redshift slices that is converted into a 3D density field, where the galaxy distribution in each slice is constructed using a statistical treatment of both spectroscopic and photometric redshifts. In this volume, we identify a proto-supercluster, dubbed “Hyperion” for its immense size and mass, which extends over a volume of ∼60 × 60 × 150 comoving Mpc3 and has an estimated total mass of ∼4.8 × 1015 M⊙. This immensely complex structure contains at least seven density peaks within 2.4 ≲ z ≲ 2.5 connected by filaments that exceed the average density of the volume. We estimate the total mass of the individual peaks, Mtot, based on their inferred average matter density, and find a range of masses from ∼0.1 × 1014 M⊙ to ∼2.7 × 1014 M⊙. By using spectroscopic members of each peak, we obtain the velocity dispersion of the galaxies in the peaks, and then their virial mass Mvir (under the strong assumption that they are virialised). The agreement between Mvir and Mtot is surprisingly good, at less than 1−2σ, considering that (almost all) the peaks are probably not yet virialised. According to the spherical collapse model, these peaks have already started or are about to start collapsing, and they are all predicted to be virialised by redshift z ∼ 0.8−1.6. We finally perform a careful comparison with the literature, given that smaller components of this proto-supercluster had previously been identified using either heterogeneous galaxy samples (Lyα emitters, sub-mm starbursting galaxies, CO emitting galaxies) or 3D Lyα forest tomography on a smaller area. With VUDS, we obtain, for the first time across the central ∼1 deg2 of the COSMOS field, a panoramic view of this large structure, that encompasses, connects, and considerably expands in a homogeneous way on all previous detections of the various sub-components. The characteristics of this exceptional proto-supercluster, its redshift, its richness over a large volume, the clear detection of its sub-components, together with the extensive multi-wavelength imaging and spectroscopy granted by the COSMOS field, provide us the unique possibility to study a rich supercluster in formation.
We imaged, with ALMA and ARGOS/LUCI, the molecular gas and dust and stellar continuum in XID2028, which is an obscured quasi-stellar object (QSO) at z = 1.593, where the presence of a massive outflow ...in the ionised gas component traced by the OIII5007 emission has been resolved up to 10 kpc. This target represents a unique test case to study QSO feedback in action at the peak epoch of AGN-galaxy co-evolution. The QSO was detected in the CO(5 − 4) transition and in the 1.3 mm continuum at ~30 and ~20σ significance, respectively; both emissions are confined in the central (<2 kpc) radius area. Our analysis suggests the presence of a fast rotating molecular disc (v ~ 400 km s−1) on very compact scales well inside the galaxy extent seen in the rest-frame optical light (~10 kpc, as inferred from the LUCI data). Adding available measurements in additional two CO transitions, CO(2 − 1) and CO(3 − 2), we could derive a total gas mass of ~1010 M⊙, thanks to a critical assessment of CO excitation and the comparison with the Rayleigh–Jeans continuum estimate. This translates into a very low gas fraction (<5%) and depletion timescales of 40–75 Myr, reinforcing the result of atypical gas consumption conditions in XID2028, possibly because of feedback effects on the host galaxy. Finally, we also detect the presence of high velocity CO gas at ~5σ, which we interpret as a signature of galaxy-scale molecular outflow that is spatially coincident with the ionised gas outflow. XID2028 therefore represents a unique case in which the measurement of total outflowing mass, of ~500–800 M⊙ yr−1 including the molecular and atomic components in both the ionised and neutral phases, was attempted for a high-z QSO.
Abstract
Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by ...measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over ∼2 deg2 of the Cosmological Evolution Survey (COSMOS) field. We split the radio source population into star-forming galaxies (SFGs) and active galactic nuclei (AGN), and further separate the AGN into radiatively efficient and inefficient accreters. Restricting our analysis to z < 1, we find SFGs have a bias, $b = 1.5 ^{+0.1}_{-0.2}$, at a median redshift of z = 0.62. On the other hand, AGN are significantly more strongly clustered with b = 2.1 ± 0.2 at a median redshift of 0.7. This supports the idea that AGN are hosted by more massive haloes than SFGs. We also find low accretion rate AGN are more clustered (b = 2.9 ± 0.3) than high accretion rate AGN ($b = 1.8^{+0.4}_{-0.5}$) at the same redshift (z ∼ 0.7), suggesting that low accretion rate AGN reside in higher mass haloes. This supports previous evidence that the relatively hot gas that inhabits the most massive haloes is unable to be easily accreted by the central AGN, causing them to be inefficient. We also find evidence that low accretion rate AGN appear to reside in halo masses of Mh ∼ 3–4 × 1013 h−1 M⊙ at all redshifts. On the other hand, the efficient accreters reside in haloes of Mh ∼ 1–2 × 1013 h−1 M⊙ at low redshift but can reside in relatively lower mass haloes at higher redshifts. This could be due to the increased prevalence of cold gas in lower mass haloes at z ≥ 1 compared to z < 1.
Context. X-ray emission from quasars (QSOs) has been used to assess supermassive black hole accretion properties up to z ≈ 6. However, at z > 6 only ≈15 QSOs are covered by sensitive X-ray ...observations, preventing a statistically significant investigation of the X-ray properties of the QSO population in the first Gyr of the Universe. Aims. We present new Chandra observations of a sample of 10 z > 6 QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy log M BH M ⊙ = 8.5 − 9.6 $ \left(\log\frac{M_{\mathrm{BH}}}{M_\odot}=8.5{-}9.6\right) $ . Adding archival X-ray data for an additional 15 z > 6 QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe. In particular, we focus on the LUV − LX relation, which is traced by the αox parameter, and the shape of their X-ray spectra. Methods. We performed photometric analyses to derive estimates of the X-ray luminosities of our z > 6 QSOs, and thus their αox values and bolometric corrections (Kbol = Lbol/LX). We compared the resulting αox and Kbol distributions with the results found for QSO samples at lower redshift, and ran several statistical tests to check for a possible evolution of the LUV − LX relation. Finally, we performed a basic X-ray spectral analysis of the brightest z > 6 QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. Results. We detect seven of the new Chandra targets in at least one standard energy band, while two more are detected discarding energies E > 5 keV, where background dominates. We confirm a lack of significant evolution of αox with redshift, which extends the results from previous works up to z > 6 with a statistically significant QSO sample. Furthermore, we confirm the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ( ⟨Γ⟩ = 2.20−0.34+0.39 ⟨ Γ ⟩ = 2 . 20 − 0.34 + 0.39 $ \langle\Gamma\rangle=2.20_{-0.34}^{+0.39} $ and ⟨Γ⟩ = 2.13−0.13+0.13 ⟨ Γ ⟩ = 2 . 13 − 0.13 + 0.13 $ \langle\Gamma\rangle=2.13_{-0.13}^{+0.13} $ for sources with < 30 and > 30 net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at z = 1 − 6. Conclusions. All of these results indicate a lack of substantial evolution of the inner accretion-disk and hot-corona structure in QSOs from low redshift to z > 6. Our data hint at generally high Eddington ratios at z > 6.
Abstract
We study the spectrophotometric properties of a highly magnified (
) pair of stellar systems identified at
z
= 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five ...multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint (
), young (
Myr), low-mass (
), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by
pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow (
km s
−1
) high-ionization lines. These features may be the signature of very hot (
K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Ly
α
emission (e.g., C
iv
/Ly
α
), despite the fact that the Ly
α
line flux is expected to be 150 times brighter (inferred from the H
β
flux). A spatially offset, strongly magnified (
) Ly
α
emission with a spatial extent
kpc
2
is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Ly
α
induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with
de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Ly
α
emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Ly
α
detection.
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