THE METALLICITY AND DUST CONTENT OF A REDSHIFT 5 GAMMA-RAY BURST HOST GALAXY

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 (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Ly alpha absorber with a very large neutral hydrogen column density of log N(H I)/cm super(-2) = 22.30 + or - 0.06 and a metallicity of [S/H] = -1.70 + or - 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 sub(V) = 0.11 + or - 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group.