Probing the H I Kinematics of the Lmc: toward Interpreting Qal Observations of Protogalactic Velocity Fields

We examine the gas kinematics of the LMC revealed by the high spatial and velocity resolution H I data cube of the combined ATCA and Parkes telescope surveys. We adopt an approach designed to facilitate comparisons with quasar absorption line observations, in particular restricting our analysis to pointings with H I column density satisfying the damped Lyα (DLA) criterion. We measure velocity widths for ≈ 5000 random pointings to the LMC and find a median value of ≈ 40 km s which modestly exceeds the value predicted by differential rotation. This median is significantly lower than the median value observed for the metal-line profiles of high z DLA. Therefore, assuming the metal-line profiles track H I kinematics, the velocity fields of high z DLA are inconsistent with the kinematics of low-mass galaxies like the LMC. We also investigate the kinematic characteristics of the giant H I shells which permeate the LMC. These shells impart an additional 10 to 20 km/s to the velocity widths in ≈ 20% of random pointings to the LMC. These non-gravitational motions are insufficient to explain the DLA kinematics even if the shells had significanlty larger covering fraction in the early universe. To account for the DLA with processes related to SN feedback requires winds with a qualitatively different nature than those observed in the LMC. Subject headings: galaxies: formation, galaxies: high-redshift, quasars: absorption lines