Exploring the host environments of long-duration gamma-ray bursts

Abstract

We have conducted the first dedicated spectroscopic survey of long-duration gamma-ray burst (LGRB) host galaxies at z < 1, and use these observations along with data from the literature to determine a wide range of ISM properties and a statistically robust mass-metallicity relation. LGRBs have been proposed as possible tracers of star formation at high redshift; however, such an association is dependent on a thorough understanding of the relationship between LGRB progenitors and their host environments. In particular, the metallicity of LGRB host galaxies has become a matter of hot debate in recent years. We conclude that LGRBs do exhibit a general trend toward lower-metallicity host galaxies, but also detect several high-metallicity hosts in our sample. We have also compared the energetic and environmental properties of the LGRBs in our sample, and find no statistically significant correlation between host metallicity and isotropic or beaming-corrected gamma-ray energy release. This is at odds with previous theoretical and observational predictions of an inverse correlation between gamma-ray energy release and host metallicity, and demonstrates that the complex role of metallicity in LGRB progenitor formation still remains unclear.