The XQR-30 Metal Absorber Catalog: 778 Absorption Systems Spanning 2 < z < 6.5

TL;DR

This paper presents a comprehensive catalog of 778 metal absorption systems from high-quality spectra of 30 quasars at redshifts 2 to 6.5, significantly expanding the dataset for studying early Universe metal enrichment.

Contribution

It introduces the XQR-30 catalog, the largest high-redshift metal absorber sample to date, with publicly available data and tools for future research.

Findings

Expanded sample of high-redshift metal absorbers, especially CIV and SiIV.

Catalog includes 778 systems spanning 2 < z < 6.5.

Provides completeness statistics and analysis tools for the community.

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 catalog of 778 systems showing absorption in one or more of MgII (360 systems), FeII (184), CII (46), CIV (479), SiIV (127), and NV (13) which span 2 < z < 6.5. This catalog significantly expands on existing samples of z > 5 absorbers, especially for CIV and SiIV which are important probes of the ionizing photon background at high redshift. The sample is 50% (90%) complete for rest-frame equivalent widths W > 0.03AA (0.09AA). We publicly release the absorber catalog along with completeness statistics and a Python script to compute the absorption search path for different ions and redshift ranges. This dataset 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 the James Webb Space Telescope and 30m-class telescopes.