Probing the H I kinematics of the large magellenic cloud: Toward interpreting quasar absorption-line observations of protogalactic velocity fields

We examine the gas kinematics of the Large Magellenic Cloud (LMC) revealed by the high spatial and velocity resolution H I data cube of the combined Australia Telescope Compact Array 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 Lyalpha (DLA) criterion. We measure velocity widths for approximate to5000 random pointings to the LMC and find a median value of approximate to40 km s(-1), 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 DLAs. Therefore, assuming that the metal-line profiles track H I kinematics, the velocity fields of high-z DLAs are inconsistent with the kinematics of low-mass galaxies such as the LMC. We also investigate the kinematic characteristics of the giant H I shells that permeate the LMC. These shells impart an additional 10-20 km s(-1) to the velocity widths in approximate to20% of random pointings to the LMC. These nongravitational motions are insufficient to explain the DLA kinematics even if the shells had significantly larger covering fraction in the early universe. To account for the DLAs with processes related to supernova feedback requires winds with a qualitatively different nature than those observed in the LMC.