Evolution of damped Lyman alpha kinematics and the effect of spatial resolution on 21-cm measurements

Abstract

We have investigated the effect of spatial resolution on determining pencil-beam-like velocity widths and column densities in galaxies. Three 21-cm data sets are used, the H I Parkes All Sky Survey (HIPASS) galaxy catalogue, a subset of HIPASS galaxies with Australia Telescope Compact Array maps and a high-resolution image of the Large Magellanic Cloud. Velocity widths measured from 21-cm emission in local galaxies are compared with those measured in intermediate-redshift damped Lyman α (DLA) absorbers. We conclude that spatial resolution has a severe effect on measuring pencil-beam like velocity widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase the median velocit..