We present deep Chandra observations of PSO J231.6576−20.8335, a quasar at redshift z = 6.59 with a nearby (∼8 proper kpc) companion galaxy. The Atacama Large Millimeter/submillimeter Array observed ...both the quasar and companion to be bright in C ii, and the system has significant extended Ly emission around the quasar, suggesting that a galaxy merger is ongoing. Unlike previous studies of two similar systems, and despite observing the system with Chandra for 140 ks, we do not detect the companion in X-rays. The quasar itself is detected, but only net counts are observed. From a basic spectral analysis, the X-ray spectrum of the quasar is soft (hardness ratio of , power-law index of ), which results in a rest-frame X-ray luminosity comparable to other bright quasars ( ) despite the faint observed X-ray flux. We highlight two possible interpretations of this result: the quasar has a steep value of Γ-potentially related to observed ongoing Eddington accretion-thereby pushing much of the emission out of our observed band, or the quasar has a more normal spectrum (Γ ∼ 2) but is therefore less X-ray luminous ( ).
Abstract
The discovery of quasars a few hundred megayears after the Big Bang represents a major challenge to our understanding of black holes as well as galaxy formation and evolution. Quasars' ...luminosity is produced by extreme gas accretion onto black holes, which have already reached masses of
M
BH
> 10
9
M
⊙
by
z
∼ 6. Simultaneously, their host galaxies form hundreds of stars per year, using up gas in the process. To understand which environments are able to sustain the rapid formation of these extreme sources, we started a Very Large Telescope/Multi-Unit Spectroscopic Explorer (MUSE) effort aimed at characterizing the surroundings of a sample of 5.7 <
z
< 6.6 quasars, which we have dubbed the Reionization Epoch QUasar InvEstigation with MUSE (REQUIEM) survey. We here present results of our searches for extended Ly
α
halos around the first 31 targets observed as part of this program. Reaching 5
σ
surface brightness limits of 0.1–1.1 × 10
−17
erg s
−1
cm
−2
arcsec
−2
over a 1 arcsec
2
aperture, we were able to unveil the presence of 12 Ly
α
nebulae, eight of which are newly discovered. The detected nebulae show a variety of emission properties and morphologies with luminosities ranging from 8 × 10
42
to 2 × 10
44
erg s
−1
, FWHMs between 300 and 1700 km s
−1
, sizes <30 pkpc, and redshifts consistent with those of the quasar host galaxies. As the first statistical and homogeneous investigation of the circumgalactic medium of massive galaxies at the end of the reionization epoch, the REQUIEM survey enables the study of the evolution of the cool gas surrounding quasars in the first 3 Gyr of the universe. A comparison with the extended Ly
α
emission observed around bright (
M
1450
≲ −25 mag) quasars at intermediate redshift indicates little variations on the properties of the cool gas from
z
∼ 6 to
z
∼ 3, followed by a decline in the average surface brightness down to
z
∼ 2.
We study the interstellar medium in a sample of 27 high-redshift quasar host galaxies at z 6, using the C ii 158 m emission line and the underlying dust continuum observed at ∼1 kpc resolution with ...Atacama Large Millimeter Array. By performing uv-plane spectral stacking of both the high and low spatial resolution data, we investigate the spatial and velocity extent of gas and the size of the dust-emitting regions. We find that the average surface brightness profile of both the C ii and the dust continuum emission can be described by a steep component within a radius of 2 kpc and a shallower component with a scale length of 2 kpc, detected up to ∼10 kpc. The surface brightness of the extended emission drops below ∼1% of the peak at radius of ∼5 kpc, beyond which it constitutes 10%-20% of the total measured flux density. Although the central component of the dust continuum emission is more compact than that of the C ii emission, the extended components have equivalent profiles. The observed extended components are consistent with those predicted by hydrodynamical simulations of galaxies with similar infrared luminosities, where the dust emission is powered by star formation. The C ii spectrum measured in the mean uv-plane stacked data can be described by a single Gaussian, with no observable C ii broad-line emission (velocities in excess of 500 km s−1), which would be indicative of outflows. Our findings suggest that we are probing the interstellar medium and associated star formation in the quasar host galaxies up to radii of 10 kpc, whereas we find no evidence for halos or outflows.
We report on 0 35 ( 2kpc) resolution observations of the C ii and dust continuum emission from five z > 6 quasar host-companion galaxy pairs obtained with the Atacama Large Millimeter/submillimeter ...Array. The C ii emission is resolved in all galaxies, with physical extents of 3.2-5.4 kpc. The dust continuum is on-average 40% more compact, which results in larger C ii deficits in the center of the galaxies. However, the measured C ii deficits are fully consistent with those found at lower redshifts. Four of the galaxies show C ii velocity fields that are consistent with ordered rotation, while the remaining six galaxies show no clear velocity gradient. All galaxies have high (∼80−200 km s−1) velocity dispersions, consistent with the interpretation that the interstellar medium (ISM) of these high-redshift galaxies is turbulent. By fitting the galaxies with kinematic models, we estimate the dynamical mass of these systems, which ranges between (0.3 − >5.4) × 1010 M . For the three closest-separation galaxy pairs, we observe dust and C ii emission from gas in between and surrounding the galaxies, which is an indication that tidal interactions are disturbing the gas in these systems. Although gas exchange in these tidal interactions could power luminous quasars, the existence of quasars in host galaxies without nearby companions suggests that tidal interactions are not the only viable method for fueling their active centers. These observations corroborate the assertion that accreting supermassive black holes do not substantially contribute to the C ii and dust continuum emission of the quasar host galaxies, and showcase the diverse ISM properties of galaxies when the universe was less than one billion years old.
A new method is used to measure the physical conditions of the gas in damped Ly alpha systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio ...of the upper and lower fine-structure levels of the ground state of C+ and Si super(+). These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ~100 cm super(-3) and temperatures below 500 K. We further find that the typical pressure of DLAs in our sample is log(P/kB) = 3.4 (K cm super(-3)), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., n sub(H) > 0.1 cm super(-3)) are required to match observations. Finally, we identify eight systems with positive detections of Si II*. These systems have pressures (P/kB) in excess of 20,000 K cm super(-3), which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.
We present high spatial resolution ( 2 kpc) Atacama Large Millimeter/submillimeter Array (ALMA) observations of C ii 158 m and dust-continuum emission from a galaxy at selected by its strong H i ...absorption (a damped Ly absorber, DLA) against a background QSO. Our ALMA images reveal a pair of star-forming galaxies separated by kpc (projected) undergoing a major merger. Between these galaxies is a third emission component with highly elevated (2×) C ii 158 m emission relative to the dust continuum, which is likely to arise from stripped gas associated with the merger. This merger of two otherwise-normal galaxies is not accompanied by enhanced star formation, contrary to mergers detected in most luminosity-selected samples. The DLA associated with the merger exhibits extreme kinematics, with a velocity width for the low-ionization metal lines of , that spans the velocity spread revealed in the C ii 158 m emission. We propose that DLAs with high values are a signpost of major mergers in normal galaxies at high redshifts, and use the distribution of the velocity widths of metal lines in high-z DLAs to provide a rough estimate the fraction of z > 3 galaxies that are undergoing a major merger.
Abstract
We report Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet and Arecibo Telescope H i 21 cm spectroscopy of six damped and sub-damped Lyman-α absorbers (DLAs and sub-DLAs, ...respectively) at z ≲ 0.1, which have yielded estimates of their H i column density, metallicity and atomic gas mass. This significantly increases the number of DLAs with gas mass estimates, allowing the first comparison between the gas masses of DLAs and local galaxies. Including three absorbers from the literature, we obtain H i masses ≈(0.24–5.2) × 109 M⊙, lower than the knee of the local H i mass function. This implies that massive galaxies do not dominate the absorption cross-section for low-z DLAs. We use Sloan Digital Sky Survey photometry and spectroscopy to identify the likely hosts of four absorbers, obtaining low stellar masses, ≈107–108.4 M⊙, in all cases, consistent with the hosts being dwarf galaxies. We obtain high H i 21 cm or CO emission line widths, ΔV20 ≈ 100–290 km s−1, and high gas fractions, fH i ≈ 5–100, suggesting that the absorber hosts are gas-rich galaxies with low star formation efficiencies. However, the H i 21 cm velocity spreads (≳100 km s−1) appear systematically larger than the velocity spreads in typical dwarf galaxies.
Abstract
We present Atacama Large Millimeter/submillimeter Array band 8 observations of the O
iii
88
μ
m line and the underlying thermal infrared continuum emission in the
z
= 6.08 quasar ...CFHQS J2100–1715 and its dust-obscured starburst companion galaxy (projected distance: ∼60 kpc). Each galaxy hosts dust-obscured star formation at rates >100
M
⊙
yr
−1
, but only the quasar shows evidence for an accreting 10
9
M
⊙
black hole. Therefore we can compare the properties of the interstellar medium in distinct galactic environments in two physically associated objects, ∼1 Gyr after the big bang. Bright O
iii
88
μ
m emission from ionized gas is detected in both systems; the positions and linewidths are consistent with earlier C
ii
measurements, indicating that both lines trace the same gravitational potential on galactic scales. The O
iii
88
μ
m/far-infrared (FIR) luminosity ratios in both sources fall in the upper range observed in local luminous infrared galaxies of similar dust temperature, although the ratio of the quasar is smaller than in the companion. This suggests that gas ionization by the quasar (expected to lead to strong optical O
iii
5008 Å emission) does not dominantly determine the quasar’s FIR O
iii
88
μ
m luminosity. Both the inferred number of photons needed for the creation of O
++
and the typical line ratios can be accounted for without invoking extreme (top-heavy) stellar initial mass functions in the starbursts of both sources.
We present the discovery of PSO J083.8371+11.8482, a weak emission line quasar with extreme star formation rate at z = 6.3401. This quasar was selected from Pan-STARRS1, UHS, and unWISE photometric ...data. Gemini/GNIRS spectroscopy follow-up indicates a Mg ii-based black hole mass of M and an Eddington ratio of , in line with an actively accreting supermassive black hole (SMBH) at z 6. Hubble Space Telescope imaging sets strong constraint on lens boosting, showing no relevant effect on the apparent emission. The quasar is also observed as a pure point source with no additional emission component. The broad-line region (BLR) emission is intrinsically weak and not likely caused by an intervening absorber. We found rest-frame equivalent widths of EW , EW (3 upper limit), and EW . A small proximity zone size ( pMpc) indicates a lifetime of only years from the last quasar phase ignition. ALMA shows extended C ii emission with a mild velocity gradient. The inferred far-infrared luminosity ( ) is one of the highest among all known quasar hosts at z 6. Dust and C ii emissions put a constraint on the star formation rate of SFR = 900- , similar to that of a hyperluminous infrared galaxy. Considering the observed quasar lifetime and BLR formation timescale, the weak-line profile in the quasar spectrum is most likely caused by a BLR that is not yet fully formed rather than by continuum boosting by gravitational lensing or a soft continuum due to super-Eddington accretion.
ABSTRACT Current observational evidence suggests that the star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in damped Ly systems (DLAs) at is more than 10 times lower than ...predicted by the Kennicutt-Schmidt (KS) relation. To understand the origin of this deficit, and to investigate possible evolution with redshift and galaxy properties, we measure the SFR efficiency of atomic gas at 1, 2, and around star-forming galaxies. We use new robust photometric redshifts in the Hubble Ultra Deep Field to create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies' outskirts. We find that the SFR efficiency of H i gas at is ∼1%-3% of that predicted by the KS relation. Contrary to simulations and models that predict a reduced SFR efficiency with decreasing metallicity and thus with increasing redshift, we find no significant evolution in the SFR efficiency with redshift. Our analysis instead suggests that the reduced SFR efficiency is driven by the low molecular content of this atomic-dominated phase, with metallicity playing a secondary effect in regulating the conversion between atomic and molecular gas. This interpretation is supported by the similarity between the observed SFR efficiency and that observed in local atomic-dominated gas, such as in the outskirts of local spiral galaxies and local dwarf galaxies.
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![Resolved [C ii] Emission fr...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_1538-4357/small "Resolved [C ii] Emission from z > 6 Quasar Host-Companion Galaxy Pairs")
