Local Column Density Distribution Function from HI selected galaxies
Abstract
The cross-section of sky occupied by a particular neutral hydrogen column density provides insight into the nature of Lyman-alpha absorption systems. We have measured this column density distribution at z=0 using 21-cm HI emission from a blind survey. A subsample of HI Parkes All Sky Survey (HIPASS) galaxies have been imaged with the Australia Telescope Compact Array (ATCA). The contribution of low HI mass galaxies 107.5 to 108 Msolar is compared to that of Mstar (1010 to 1010.5 Msolar) galaxies. We find that the column density distribution function is dominated by low HI mass galaxies with column densities in the range 3x1018 to 2x1020 cm-2. This result is not intuitively obvious. Mstar galaxies may contain the bulk of the HI gas, but the cross-section presented by low HI mass galaxies 107.5 to 108 Msolar is greater at moderate column densities. This result implies that moderate column density Lyman-alpha absorption systems may be caused by a range of galaxy types and not just large spiral galaxies as originally thought.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.