2013•arXiv (Cornell University)Open access
Two high-redshift DLAs towards a z~5 gamma-ray burst
Martin Sparre, O. E. Hartoog, T. Krühler, J. P. U. Fynbo, D. Watson, K. Wiersema, V. D’Elia, A. De, P. Afonso, S. Covino, A. de Ugarte Postigo, H. Flores, P. Goldoni, J. Greiner, J. Hjorth, P. Jakobsson, L. Kaper, S. Klose, D. Malesani, B. Milvang‐Jensen, M. Nardini, S. Piranomonte, J. Sollerman, R. Sánchez-Ramírez, S. Schulze, N. R. Tanvir, S. D. Vergani, R. A. M. J. Wijers, Tayyaba Zafar
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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.