21 - Evolution of dust and elemental abundances in quasar DLAs and GRB afterglows as a function of cosmic time

Summary

We present results from comparisons of elemental abundances and dust content between damped Lyman-alpha (DLA) absorbers and gamma-ray-burst (GRB) afterglows, as determined by absorption-line spectroscopy. Our sample of DLA absorbers includes the results from 76 quasar spectra taken with the HIRES spectrograph of the Keck observatory, from which we obtain a sample of 38 DLA absorbers in the redshift range 2 < z < 4. The GRB absorption lines were obtained in collaboration with the Caltech Carnegie NOAO GRB collaboration, in which rapid spectroscopy is obtained from newly discovered GRBs, to obtain high-quality optical spectra. We present results of O, N, C, Si, Zn, Cr, and C II^*/C II ratios from a “core sample” of 15 of the best of the DLA absorbers, and detailed analysis of GRB 051111 and GRB 050505, which are at redshifts of z = 1.549 and 4.275, respectively. From our analysis we can see trends in the DLA dust content, and in [C/H], [N/H] and [O/H] values as a function of DLA redshift, as well as evidence for dust formation and highly excited dense gas within the disks of GRB host galaxies.