ABSTRACT. We analyze the gas kinematics of damped Lyα systems (DLAs) hosting high-z gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs), focusing on three statistics: (1) Δv₉₀, the velocity interval encompassing 90% of the integrated optical depth, and (2) W₁₅₂₆ and (3) W₁₅₄₈, the rest equivalent widths of the Si II 1526 and C IV 1548 transitions, respectively. The Δv₉₀ distributions of the GRB-DLAs and QSO-DLAs are similar; each has median Δv₉₀ 80 km s⁻¹ and a significant tail, extending to several hundred km s⁻¹. This suggests comparable galaxy masses for the parent populations of GRB-DLAs and QSO-DLAs, and we infer that the average dark matter halo mass of GRB galaxies is 10¹² M. The unique configuration of GRB-DLA sight lines and the presence (and absence) of fine-structure absorption together give special insight into the nature of high-z protogalactic velocity fields. The data support a scenario in which the Δv₉₀ statistic reflects dynamics in the interstellar medium (ISM) and W₁₅₂₆ traces motions outside the ISM (e.g., halo gas and galactic-scale winds). The W₁₅₂₆ statistic and gas metallicity [M/H] are tightly correlated, especially for the QSO-DLAs: [M/H] = a + blog(W₁₅₂₆/1Å) with a = −0.92 ± 0.05 and b = 1.41 ± 0.10. We argue that the W₁₅₂₆ statistic primarily tracks dynamical motions in the halos of high-z galaxies and interpret this correlation as a mass-metallicity relation with very similar slope to the trend observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit systematically larger W₁₅₂₆ values (>0.5 Å) than the QSO-DLAs (W₁₅₂₈ 0.5 Å), which may suggest that galactic-scale outflows contribute to the largest observed velocity fields.

Subject headings: quasars: absorption lines

Print publication: Issue 1 (2008 January 1)
Received 2007 March 27, accepted for publication 2007 August 31