The cosmic evolution of dust-corrected metallicity in the neutral gas^★

¹ European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
e-mail: adecia@eso.org
² European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
³ IAP, CNRS and Université Paris 6, 98bis boulevard Arago, 75014 Paris, France
⁴ Physics Dept., University of Calabria, via P. Bucci, 87036 Arcavacata di Rende, Italy

Received: 19 September 2017
Accepted: 7 December 2017

Abstract

Interpreting abundances of damped Ly-α absorbers (DLAs) from absorption-line spectroscopy has typically been a challenge because of the presence of dust. Nevertheless, because DLAs trace distant gas-rich galaxies regardless of their luminosity, they provide an attractive way of measuring the evolution of the metallicity of the neutral gas with cosmic time. This has been done extensively so far, but typically not taking proper dust corrections into account. The aims of this paper are to: (i) provide a simplified way of calculating dust corrections, based on a single observed [X/Fe], (ii) assess the importance of dust corrections for DLA metallicities and their evolution, and (iii) investigate the cosmic evolution of iron for a large DLA sample. We have derived dust corrections based on the observed [Zn/Fe], [Si/Fe], or [S/Fe], and confirmed their robustness. We present dust-corrected metallicities in a scale of [Fe/H]_tot for 236 DLAs over a broad range of z, and assess the extent of dust corrections for different metals at different metallicities. Dust corrections in DLAs are important even for Zn (typically of 0.1–0.2, and up to 0.5 dex), which is often neglected. Finally, we study the evolution of the dust-corrected metallicity with z. The DLA metallicities decrease with redshift, by a factor of 50–100 from today to ~12.6 billion years ago (z = 5). When including dust corrections, the average DLA metallicities are 0.4–0.5 dex higher than without corrections. The upper envelope of the relation between metallicity and z reaches solar metallicity at z ≲ 0.5, although some systems can have solar metallicity already out to z ~ 3.