The H i column density distribution function in faint dwarf galaxies

This is the authors' abstract. We don't add key points for this paper.

We present the HI column density distribution function,f (N HI ), as measured from dwarf galaxies observed as part of the Faint Irregular Galaxy GMRT (FIGGS) survey.We find that the shape of the dwarf galaxy f (N HI ) is significantly different from the f (N HI ) for high redshift Damped Lyman -α absorbers (DLAs) or the f (N HI ) for a representative sample of z = 0 gas rich galaxies.The dwarf f (N HI ) falls much more steeply at high HI column densities as compared to the other determinations.While ∼ 10% of the cross section above N HI = 10 20.3 atoms cm -2 at z = 0 is provided by dwarf galaxies, the fraction falls to 1% by N HI ∼ 10 21.5 atoms cm -2 .In the local universe, the contribution to the high N HI end of the f (N HI ) distribution comes predominantly from the inclined disks of large galaxies.Dwarf galaxies, both because of their smaller scale lengths, and their larger intrinsic axial ratios do not produce large HI column densities even when viewed edge-on.If high column density DLAs/GRB hosts correspond to galaxies like the local dwarfs, this would require either that (i) the absorption arises from merging and not isolated systems or (ii) the observed lines of sight are strongly biased towards high column density regions.