On the Nature of Velocity Fields in High-z Galaxies

• Published in: The Astrophysical journal Vol. 672; no. 1; pp. 59 - 71
• Main Authors: Prochaska, Jason X, Chen, Hsiao-Wen, Wolfe, Arthur M, Dessauges-Zavadsky, Miroslava, Bloom, Joshua S
• Format: Journal Article
• Language: English
• Published: Chicago, IL IOP Publishing 01.01.2008; University of Chicago Press
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Quasars; High field; Absorption line; Galaxies; quasars: absorption lines; Velocity fields
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/523689

We analyze the gas kinematics of damped Ly alpha systems (DLAs) hosting high-z gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs), focusing on three statistics: (1) Delta [unk], 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 Delta [unk] distributions of the GRB-DLAs and QSO-DLAs are similar; each has median Delta [unk] approximately 80 km s super(-1) and a significant tail, extending to several hundred km s super(-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 [unk]10 super(12) M [unk]. 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 Delta [unk] 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] = alpha + beta log (W1526/ [unk]) with alpha = -0.92 plus or minus 0.05 and beta = 1.41 plus or minus 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 AA) than the QSO-DLAs ((W1526) approximately 0.5 AA), which may suggest that galactic-scale outflows contribute to the largest observed velocity fields.