The metallicity and dust content of a redshift 5 gamma-ray burst host galaxy

TL;DR

This study presents detailed measurements of the metallicity, dust content, and chemical properties of a gamma-ray burst host galaxy at redshift 5, providing insights into early universe galaxy composition.

Contribution

It reports the highest redshift GRB host galaxy with precise metallicity and dust measurements, including the first detection of Fe II fine-structure lines at this redshift.

Findings

Host galaxy has high neutral hydrogen column density (log N(HI)=22.30)

Metallicity measured at [S/H]= -1.70, the highest at this redshift with such precision

Dust-to-metals ratio is comparable to or lower than local universe values

Abstract

Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio and extinction of the GRB host galaxy at z=5.0. The host absorption system is a damped Lyman-alpha absorber (DLA) with a very large neutral hydrogen column density of log N(HI)/cm^(-2) = 22.30 +/- 0.06, and a metallicity of [S/H]= -1.70 +/- 0.10. It is the highest redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z=5.0 system as the GRB host galaxy, and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A_V = 0.11 +/- 0.04 mag, and the host galaxy has a dust-to-metals ratio which is consistent with being equal to or lower than typical values in the Local Group.