Open AccessThe column density distribution function at z = 0 from H i selected galaxies
Author(s) -
RyanWeber Emma V.,
Webster Rachel L.,
StaveleySmith Lister
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06754.x
Subject(s) - physics , astrophysics , galaxy , redshift , spiral galaxy , power law , astronomy , statistics , mathematics
We have measured the column density distribution function, f ( N H i ) , at z = 0 using 21‐cm H i emission from galaxies selected from a blind H i survey. f ( N H i ) is found to be smaller and flatter at z = 0 than indicated by high‐redshift measurements of damped Lyman α (DLA) systems, consistent with the predictions of hierarchical galaxy formation. The derived DLA number density per unit redshift, d N DLA /d z = 0.058 , is in moderate agreement with values calculated from low‐redshift QSO absorption line studies. We use two different methods to determine the types of galaxies which contribute most to the DLA cross‐section: comparing the power‐law slope of f ( N H i ) to theoretical predictions and analysing contributions to d N DLA /d z . We find that comparison of the power‐law slope cannot rule out spiral discs as the dominant galaxy type responsible for DLA systems. Analysis of d N DLA /d z however, is much more discriminating. We find that galaxies with log M H i < 9.0 make up 34 per cent of d N DLA /d z ; Irregular and Magellanic types contribute 25 per cent; galaxies with surface brightness account for 22 per cent and sub‐ L * galaxies contribute 45 per cent to d N DLA /d z . We conclude that a large range of galaxy types give rise to DLA systems, not just large spiral galaxies as previously speculated.