E-XQR-30: The evolution of Mg <scp>ii</scp>, C <scp>ii</scp>, and O <scp>i</scp> across 2 &lt; <i>z</i> &lt; 6
Alma Maria Sebastian, Emma Ryan‐Weber, R. L. Davies, George D. Becker, Laura C. Keating, V. D’Odorico, R. A. Meyer, Sarah E. I. Bosman, G. Cupani, Girish Kulkarni, Martin G. Haehnelt, Samuel Lai, Anna–Christina Eilers, M. Bischetti, S. Gallerani
Abstract
ABSTRACT Intervening metal absorbers in quasar spectra at z &gt; 6 can be used as probes to study the chemical enrichment of the Universe during the Epoch of Reionization. This work presents the comoving line densities (dn/dX) of low-ionization absorbers, namely, Mg ii (2796 Å), C ii (1334 Å), and O i (1302 Å) across 2 &lt; z &lt; 6 using the E-XQR-30 metal absorber catalogue prepared from 42 XSHOOTER quasar spectra at 5.8 &lt; z &lt; 6.6. Here, we analyse 280 Mg ii (1.9 &lt; z &lt; 6.4), 22 C ii (5.2 &lt; z &lt; 6.4), and 10 O i (5.3 &lt; z &lt; 6.4) intervening absorbers, thereby building up on previous studies with improved sensitivity of 50 per cent completeness at an equivalent width of W &gt; 0.03 Å. For the first time, we present the comoving line densities of 131 weak (W &lt; 0.3 Å) intervening Mg ii absorbers at 1.9 &lt; z &lt; 6.4 which exhibit constant evolution with redshift similar to medium (0.3 &lt; W &lt; 1.0 Å) absorbers. However, the cosmic mass density of Mg ii – dominated by strong Mg ii systems – traces the evolution of global star formation history from redshift 1.9 to 5.5. E-XQR-30 also increases the absorption path-length by a factor of 50 per cent for C ii and O i whose line densities show a rising trend towards z &gt; 5, in agreement with previous works. In the context of a decline in the metal enrichment of the Universe at z &gt; 5, the overall evolution in the incidence rates of absorption systems can be explained by a weak – possibly soft fluctuating – ultraviolet background. Our results, thereby, provide evidence for a late reionization continuing to occur in metal-enriched and therefore, biased regions in the Universe.