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Abstract We use the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array to detect CO(1–0), CO(3–2), and rest-frame 349 GHz continuum emission from an Hi-selected galaxy, DLA1020+2733g, atz ≈ 2.3568 in the field of thez= 2.3553 damped Lyαabsorber (DLA) toward QSO J1020+2733. The VLA CO(1–0) detection yields a molecular gas mass of (2.84 ± 0.42) × 10¹¹ × (α_CO/4.36)M_⊙, the largest ever measured in an Hi-selected galaxy. The DLA metallicity is +0.28 ± 0.16, from the Zniiλ2026 absorption line detected in a Keck Echellette Spectrograph and Imager spectrum. This continues the trend of high-metallicity DLAs being frequently associated with massive galaxies. We obtain a star formation rate (SFR) of ≲400M_⊙yr⁻¹from the rest-frame 349 GHz continuum emission and a relatively long molecular gas depletion timescale of ≳0.6 Gyr. The excitation of theJ= 3 rotational level is subthermal, with $r_{31}\equiv L{\prime }_{\mathrm{CO}(3-2)}/L{\prime }_{\mathrm{CO}(1-0)}=0.513\pm 0.081$, suggesting that DLA1020+2733g has a low SFR surface density. The large velocity spread of the CO lines, ≈500 km s⁻¹, and the long molecular gas depletion timescale suggest that DLA1020+2733g is likely to be a cold rotating-disk galaxy. 

ABSTRACT The attenuation of Lyα photons by neutral hydrogen in the intergalactic medium (IGM) at z ≳ 5 continues to be a powerful probe for studying the epoch of reionization. Given a framework to estimate the intrinsic (true) Lyα emission of high-z sources, one can infer the ionization state of the IGM during reionization. In this work, we use the enlarged XQR-30 sample of 42 high-resolution and high signal-to-noise quasar spectra between $$5.8\lesssim \, z\lesssim \, 6.6$$ obtained with VLT/X-shooter to place constraints on the IGM neutral fraction. This is achieved using our existing Bayesian QSO reconstruction framework which accounts for uncertainties such as the: (i) posterior distribution of predicted intrinsic Lyα emission profiles (obtained via covariance matrix reconstruction of the Lyα and N v emission lines from unattenuated high-ionization emission line profiles; C iv, Si iv  + O iv], and C iii]) and (ii) distribution of ionized regions within the IGM using synthetic damping wing profiles drawn from a 1.63 Gpc3 reionization simulation. Following careful quality control, we used 23 of the 42 available QSOs to obtain constraints/limits on the IGM neutral fraction during the tail-end of reionization. Our median and 68th percentile constraints on the IGM neutral fraction are: $$0.20\substack{+0.14 -0.12}$$ and $$0.29\substack{+0.14 -0.13}$$ at z = 6.15 and 6.35. Further, we also report 68th percentile upper limits of $$\bar{x}_{\mathrm{H\, {\small I}}{}} \lt 0.21$$, 0.20, 0.21, and 0.18 at z = 5.8, 5.95, 6.05, and 6.55. These results imply reionization is still ongoing at $$5.8\lesssim \, z\lesssim \, 6.55$$, consistent with previous results from XQR-30 (dark fraction and Lyα forest) along with other observational probes considered in the literature. 

We present bolometric luminosities, black hole masses, and Eddington ratios for 42 luminous quasars at z  ≳ 6 using high signal-to-noise ratio VLT/X-shooter spectra, acquired as part of the enlarged ESO Large Programme XQR-30 . In particular, we derived the bolometric luminosities from the rest-frame 3000 Å luminosities using a bolometric correction from the literature, as well as the black hole masses by modeling the spectral regions around the C  IV 1549 Å and the Mg  II 2798 Å emission lines, with scaling relations calibrated in the Local Universe. We find that the black hole masses derived from both emission lines are in the same range and the scatter of the measurements agrees with expectations from the scaling relations. The Mg  II -derived masses are between ∼(0.8−12) ×10 9   M ⊙ and the derived Eddington ratios are within ∼0.13−1.73, with a mean (median) of 0.84(0.72). By comparing the total sample of quasars at z  > 5.8, from this work and from the literature, to a bolometric luminosity distribution-matched sample at z  ∼ 1.5, we find that quasars at high redshift host slightly less massive black holes, which accrete slightly more rapidly than those at lower z , with a difference in the mean Eddington ratios of the two samples of ∼0.27. These findings are in agreement with the results of recent works in the literature. 

ABSTRACT Intervening C iv absorbers are key tracers of metal-enriched gas in galaxy haloes over cosmic time. Previous studies suggest that the C iv cosmic mass density ($$\Omega _{\rm C \, \small {IV}}$$) decreases slowly over 1.5 $$\lesssim \, z\lesssim$$ 5 before declining rapidly at z ≳ 5, but the cause of this downturn is poorly understood. We characterize the $$\Omega _{\rm C \, \small {IV}}$$ evolution over 4.3 ≲ z ≲ 6.3 using 260 absorbers found in 42 XSHOOTER spectra of z ∼ 6 quasars, of which 30 come from the ESO Large Program XQR-30. The large sample enables us to robustly constrain the rate and timing of the downturn. We find that $$\Omega _{\rm C \, \small {IV}}$$ decreases by a factor of 4.8 ± 2.0 over the ∼300 Myr interval between z ∼ 4.7 and ∼5.8. The slope of the column density (log N) distribution function does not change, suggesting that C iv absorption is suppressed approximately uniformly across 13.2 ≤ log N/cm−2 < 15.0. Assuming that the carbon content of galaxy haloes evolves as the integral of the cosmic star formation rate density (with some delay due to stellar lifetimes and outflow travel times), we show that chemical evolution alone could plausibly explain the fast decline in $$\Omega _{\rm C \, \small {IV}}$$ over 4.3 ≲ z ≲ 6.3. However, the C iv/C ii ratio decreases at the highest redshifts, so the accelerated decline in $$\Omega _{\rm C \, \small {IV}}$$ at z ≳ 5 may be more naturally explained by rapid changes in the gas ionization state driven by evolution of the UV background towards the end of hydrogen reionization. 

ABSTRACT Intervening metal absorption lines in the spectra of z ≳ 6 quasars are fundamental probes of the ionization state and chemical composition of circumgalactic and intergalactic gas near the end of the reionization epoch. Large absorber samples are required to robustly measure typical absorber properties and to refine models of the synthesis, transport, and ionization of metals in the early Universe. The Ultimate XSHOOTER legacy survey of quasars at z ∼ 5.8–6.6 (XQR-30) has obtained high signal-to-noise spectra of 30 luminous quasars, nearly quadrupling the existing sample of 12 high quality z ∼ 6 quasar spectra. We use this unprecedented sample to construct a catalogue of 778 systems showing absorption in one or more of Mg ii (360 systems), Fe ii (184), C ii (46), C iv (479), Si iv (127), and N v (13) which span 2 ≲ z ≲ 6.5. This catalogue significantly expands on existing samples of z ≳ 5 absorbers, especially for C iv and Si iv which are important probes of the ionizing photon background at high redshift. The sample is 50 per cent (90 per cent) complete for rest-frame equivalent widths W ≳ 0.03 Å (0.09 Å). We publicly release the absorber catalogue along with completeness statistics and a python script to compute the absorption search path for different ions and redshift ranges. This data set is a key legacy resource for studies of enriched gas from the era of galaxy assembly to cosmic noon, and paves the way for even higher redshift studies with JWST and 30 m-class telescopes. 

ABSTRACT We investigate the abundance and distribution of metals in the high-redshift intergalactic medium and circum-galactic medium through the analysis of a sample of almost 600 Si iv absorption lines detected in high- and intermediate-resolution spectra of 147 quasars. The evolution of the number density of Si iv lines, the column density distribution function, and the cosmic mass density are studied in the redshift interval 1.7 ≲ z ≲ 6.2 and for log N(Si iv) ≥ 12.5. All quantities show a rapid increase between z ∼ 6 and z ≲ 5 and then an almost constant behaviour to z ∼ 2 in very good agreement with what is already observed for C iv absorption lines. The present results are challenging for numerical simulations: When simulations reproduce our Si iv results, they tend to underpredict the properties of C iv, and when the properties of C iv are reproduced, the number of strong Si iv lines [log N(Si iv) > 14] is overpredicted.