Properties of a Gamma Ray Burst Host Galaxy at z ~ 5

TL;DR

This paper analyzes the properties of a high-redshift gamma-ray burst host galaxy at z ~ 5, revealing its metallicity and implications for star formation studies using GRB observations.

Contribution

It provides detailed metallicity measurements of a rare high-redshift GRB host galaxy, highlighting potential biases in star formation inference from GRB data.

Findings

Metallicity exceeds a tenth of solar in the host galaxy.

Neutral hydrogen column density is log 21.0--21.2 cm^-2.

Metal lines indicate [Fe/H] > -0.8.

Abstract

We describe the properties of the host galaxy of the gamma-ray burst GRB060510B based on a spectrum of the burst afterglow obtained with the Gemini North 8m telescope. The galaxy lies at a redshift of z = 4.941 making it the fourth highest spectroscopically identified burst host. However, it is the second highest redshift galaxy for which the quality of the spectrum permits a detailed metallicity analysis. The neutral hydrogen column density has a logarithmic value of 21.0--21.2 cm^-2 and the weak metal lines of Ni, S and Fe show that the metallicity is in excess of a tenth of solar which is far above the metallicities in damped Lyman alpha absorbers at high redshift. The tightest constraint is from the Fe lines which place [Fe/H] in excess of -0.8. We argue that the results suggest that metallicity bias could be a serious problem with inferring star formation from the GRB population and consider how future higher quality measurements could be used to resolve this question.