GRB host galaxies with VLT/X-Shooter: properties at 0.8 < z < 1.3

TL;DR

This study uses VLT/X-Shooter spectra to analyze properties of six GRB host galaxies at 0.8 < z < 1.3, revealing that their metallicities and star formation rates align with general star-forming galaxies at similar redshifts, highlighting differences from low-redshift hosts.

Contribution

First detailed spectroscopic analysis of six GRB hosts at 0.8 < z < 1.3, providing constraints on metallicity, dust extinction, and star formation rates, and comparing them to broader galaxy populations.

Findings

GRB hosts at 0.8 < z < 1.3 have metallicities and SFRs similar to other star-forming galaxies at the same redshift.

Measured metallicities are well constrained for four hosts, supporting existing relations.

GRB hosts at these redshifts do not differ substantially from the general galaxy population.

Abstract

Long gamma-ray bursts (LGRBs) are associated with the death of massive stars. Their host galaxies therefore represent a unique class of objects tracing star formation across the observable Universe. Indeed, recently accumulated evidence shows that GRB hosts do not differ substantially from general population of galaxies at high (z > 2) redshifts. However, it has been long recognised that the properties of z < 1.5 hosts, compared to general star-forming population, are unusual. To better understand the reasons for the supposed difference in LGRB hosts properties at z < 1.5, we obtained VLT/X- Shooter spectra of six hosts lying in the redshift range of 0.8 < z < 1.3. Some of these hosts have been observed before, yet we still lack well constrained information on their characteristics such as metallicity, dust extinction and star formation rate. We search for emission lines in the VLT/X-Shooter spectra of the hosts and measure their fluxes. We perform a detailed analysis, estimating host average extinction, star-formation rates, metallicities and electron densities where possible. Measured quantities of our hosts are compared to a larger sample of previously observed GRB hosts at z < 2. Star-formation rates and metallicities are measured for all the hosts analyzed in this paper and metallicities are well determined for 4 hosts. The mass-metallicity relation, the fundamental metallicity relation and SFRs derived from our hosts occupy similar parameter space as other host galaxies investigated so-far at the same redshift. We therefore conclude that GRB hosts in our sample support the found discrepancy between the properties of low-redshift GRB hosts and the general population of star- forming galaxies.