DLA and sub-DLA metallicity evolution: A case study of absorbers towards Q0338-0005

Abstract

The damped and sub-damped Lyman alpha systems (DLAs and sub-DLAs) traced in absorption against bright background quasars represent the main reserve of neutral hydrogen at high redshifts. We used the archival Very Large Telescope (VLT) instrument Ultraviolet and Visual Echelle Spectrograph (UVES) high-resolution data of Q0338-0005 (zem = 3.049) to study abundances of the DLA (zabs = 2.2298) and sub-DLA (zabs =2.7457) along the line of sight. We estimated column densities of HI and various elements present in the DLA and sub-DLA through Voigt profile fitting. The DLA trough shows the Lyman alpha emission from its host galaxy. We derive the metallicities of the DLA and sub-DLA with [Zn/H] = -0.67 +/- 0.18 and [S/H] = -1.45 +/-0.17, respectively. We compared our abundances of the DLA and sub-DLA with other high resolution DLA and sub-DLA metallicities and find that both populations show an overall increase of metallicity with decreasing redshift. However, sub-DLAs usually have higher metallicities than the DLAs.