New Magellan Inamori Kyocera Echelle Observations of z<1.5 sub-damped Lyman-alpha systems

TL;DR

This study presents new abundance measurements in sub-Damped Lyman-alpha systems at redshifts below 1.5, revealing higher metallicities than typical DLAs and providing insights into the chemical evolution of high-redshift galaxies.

Contribution

It reports the first detailed abundance analysis of nine sub-DLAs and one DLA using MIKE spectra, highlighting metallicity differences and element ratios at low redshift.

Findings

Sub-DLAs show higher metallicity than DLAs at similar redshifts.

Detection of Zn indicates near-solar metallicity in some systems.

[Mn/Fe] increases with metallicity, consistent with Milky Way trends.

Abstract

The Damped and sub-Damped Lyman-alpha (DLA and sub-DLA) systems seen in the spectra of QSOs offer a unique way to study the interstellar medium of high redshift galaxies. In this paper we report on new abundance determinations in a sample of 10 new systems, nine of the lesser studied sub-DLAs and one DLA, along the line of sight to seven QSOs from spectra taken with the MIKE spectrograph. Lines of Mg I, Mg II, Al II, Al III, Ca II, Mn II, Fe II, and Zn II were detected. Here, we give the column densities and equivalent widths of the observed absorption lines, as well as the abundances determined for these systems. Zn, a relatively undepleted element in the local interstellar medium (ISM) is detected in one system with a high metallicity of [Zn/H]=+0.27\pm0.18. In one other system, a high abundance based on the more depleted element Fe is seen with [Fe/H]=-0.37\pm0.13, although Zn is not detected. The N(HI)-weighted mean metallicity of these sub-DLA systems based on Fe is <[Fe/H]>=-0.76\pm0.11, nearly ~0.7 dex higher (a factor of 5) than what is seen in DLAs in this redshift range. The relative abundance of [Mn/Fe] is also investigated. A clear trend is visible for these systems as well as systems from the literature, with [Mn/Fe] increasing with increasing metallicity in good agreement with with Milky Way stellar abundances.