Mass and metallicity scaling relations of high redshift star-forming galaxies selected by GRBs

TL;DR

This study examines the relationships between gas kinematics, metallicity, and stellar mass in 82 GRB-selected galaxies, revealing that velocity widths are proxies for stellar mass and that emission line metallicities have less scatter than absorption line measurements.

Contribution

It provides the first comprehensive comparison of emission and absorption metallicity measurements in GRB hosts and analyzes their relation to stellar mass across a broad redshift range.

Findings

Velocity widths correlate with stellar mass.

Emission line metallicities show less scatter than absorption line metallicities.

GRB hosts follow the mass-metallicity relation with a slight offset.

Abstract

We present a comprehensive study of the relations between gas kinematics, metallicity, and stellar mass in a sample of 82 GRB-selected galaxies using absorption and emission methods. We find the velocity widths of both emission and absorption profiles to be a proxy of stellar mass. We also investigate the velocity-metallicity correlation and its evolution with redshift and find the correlation derived from emission lines to have a significantly smaller scatter compared to that found using absorption lines. Using 33 GRB hosts with measured stellar mass and metallicitiy, we study the mass-metallicity relation for GRB host galaxies in a stellar mass range of $10^{8.2} M_{\odot}$ to $10^{11.1} M_{\odot}$ and a redshift range of $ z\sim 0.3-3.4$. The GRB-selected galaxies appear to track the mass-metallicity relation of star forming galaxies but with an offset of 0.15 towards lower metallicities. This offset is comparable with the average error-bar on the metallicity measurements of the GRB sample and also the scatter on the MZ relation of the general population. It is hard to decide whether this relatively small offset is due to systematic effects or the intrinsic nature of GRB hosts. We also investigate the possibility of using absorption-line metallicity measurements of GRB hosts to study the mass-metallicity relation at high redshifts. Our analysis shows that the metallicity measurements from absorption methods can significantly differ from emission metallicities and assuming identical measurements from the two methods may result in erroneous conclusions.