Spectroscopy of GRB 051111 at z = 1.54948: Kinematics and elemental abundances of the GRB environment and host galaxy

We present a high-resolution, high S/N optical spectrum of the afterglow of GRB 051111 obtained with the HIRES spectrograph on the Keck I 10 m telescope. The spectrum exhibits three redshitted absorption systems with the highest, at z = 1.54948, arising in the GRB host galaxy. While the Lya feature is outside the range of our spectrum, the high column density of weakly depleted Zn suggests that the host is a damped Lyα system with N(H I) ≲ 10²¹ (Z/Z_⊙)^-1. The bulk of the gas (>80%) is confined to a narrow velocity range of |v| < 30 km s^-1, exhibiting strong dust depletion of refractory elements such as Fe and Cr. The depletion pattern is similar to that observed in warm disk clouds of the Milky Way. We also detect absorption from all ground-level fine-structure states of Fe II, the first such example in a QSO-DLA system or GRB-absorption spectrum, which indicate conditions that are consistent with the "warm disk" depletion pattern. The absorption profiles of Fe II and Mg n extend over several hundred km s ^-1, with a depletion pattern that more closely resembles that of QSO-DLA systems, suggesting that the sight line to GRB 051111 probes the halo of the host galaxy in addition to the dense disk. Thus, detailed diagnostics of the interstellar medium of GRB host galaxies continue to provide insight into regions that are generally missed in quasar surveys.