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ABSTRACT We assemble the largest C iv absorption line catalogue to date, leveraging machine learning, specifically Gaussian processes, to remove the need for visual inspection for detecting C iv absorbers. The catalogue contains probabilities classifying the reliability of the absorption system within a quasar spectrum. Our training set was a sub-sample of DR7 spectra that had no detectable C iv absorption in a large visually inspected catalogue. We used Bayesian model selection to decide between our continuum model and our absorption-line models. Using a random hold-out sample of 1301 spectra from all of the 26 030 investigated spectra in DR7 C iv catalogue, we validated our pipeline and obtained an 87 per cent classification performance score. We found good purity and completeness values, both $$\sim 80{{\ \rm per\ cent}}$$, when a probability of $$\sim 95{{\ \rm per\ cent}}$$ is used as the threshold. Our pipeline obtained similar C iv redshifts and rest equivalent widths to our training set. Applying our algorithm to 185 425 selected quasar spectra from SDSS DR12, we produce a catalogue of 113 775 C iv doublets with at least 95 per cent confidence. Our catalogue provides maximum a posteriori values and credible intervals for C iv redshift, column density, and Doppler velocity dispersion. We detect C iv absorption systems with a redshift range of 1.37–5.1, including 33 systems with a redshift larger than 5 and 549 absorbers systems with a rest equivalent width greater than 2 Å at more than 95 per cent confidence. Our catalogue can be used to investigate the physical properties of the circumgalactic and intergalactic media. 

ABSTRACT This paper presents a newly established sample of 19 unique galaxies and galaxy groups at redshift z = 0.89–1.21 in six QSO fields from the Cosmic Ultraviolet Baryon Survey (CUBS), designated as the CUBSz1 sample. In this sample, nine galaxies or galaxy groups show absorption features, while the other 10 systems exhibit 2σ upper limits of $$\log N (\rm{He\,{\small I}})/\mbox{$${\rm cm^{-2}}$$}\lesssim 13.5$$ and $$\log N (\rm{O\,{\small V}})/\mbox{$${\rm cm^{-2}}$$}\lesssim 13.3$$. Environmental properties of the galaxies, including galaxy overdensities, the total stellar mass and gravitational potential summed over all neighbours, and the presence of local ionizing sources, are found to have a significant impact on the observed CGM absorption properties. Specifically, massive galaxies and galaxies in overdense regions exhibit a higher rate of incidence of absorption. The CGM absorption properties in galaxy groups appear to be driven by the galaxy closest to the QSO sightline, rather than by the most massive galaxy or by mass-weighted properties. We introduce a total projected gravitational potential ψ, defined as −ψ/G = ∑Mhalo/dproj summed over all group members, to characterize the galaxy environment. This projected gravitational potential correlates linearly with the maximum density detected in each sightline (i.e. a power-law slope of $$0.95_{-0.14}^{+0.15}$$), consistent with higher pressure gas being confined in deeper gravitational potential wells. In addition, we find that the radial profile of cool gas density exhibits a decline from the inner regions to the outskirts, and the amplitude is consistent with the cool gas being in pressure balance with the hot halo. Finally, we note that the ionizing flux from nearby galaxies can elevate the N(H i)/N(He i) ratio, which provides a unique diagnostic of possible local sources contributing to the ionizing radiation field. 

Abstract The bimodal absorption system imaging campaign (BASIC) aims to characterize the galaxy environments of a sample of 36 Hi-selected partial Lyman limit systems (pLLSs) and Lyman limit systems (LLSs) in 23 QSO fields atz≲ 1. These pLLSs/LLSs provide a unique sample of absorbers with unbiased and well-constrained metallicities, allowing us to explore the origins of metal-rich and low-metallicity circumgalactic medium (CGM) atz< 1. Here we present Keck/KCWI and Very Large Telescope/MUSE observations of 11 of these QSO fields (19 pLLSs) that we combine with Hubble Space Telescope/Advanced Camera for Surveys imaging to identify and characterize the absorber-associated galaxies at 0.16 ≲z≲ 0.84. We find 23 unique absorber-associated galaxies, with an average of one associated galaxy per absorber. For seven absorbers, all with <10% solar metallicities, we find no associated galaxies with $\log M_{\star }\gtrsim 9.0$withinρ/R_virand ∣Δv∣/v_esc≤ 1.5 with respect to the absorber. We do not find any strong correlations between the metallicities or Hicolumn densities of the gas and most of the galaxy properties, except for the stellar mass of the galaxies: the low-metallicity ([X/H] ≤ −1.4) systems have a probability of ${0.39}_{-0.15}^{+0.16}$for having a host galaxy with $\log M_{\star }\ge 9.0$withinρ/R_vir≤ 1.5, while the higher metallicity absorbers have a probability of ${0.78}_{-0.13}^{+0.10}$. This implies metal-enriched pLLSs/LLSs atz< 1 are typically associated with the CGM of galaxies with $\log M_{\star }>9.0$, whereas low-metallicity pLLSs/LLSs are found in more diverse locations, with one population arising in the CGM of galaxies and another more broadly distributed in overdense regions of the universe. Using absorbers not associated with galaxies, we estimate the unweighted geometric mean metallicity of the intergalactic medium to be [X/H] ≲ −2.1 atz< 1, which is lower than previously estimated.