The 1000 Brightest HIPASS Galaxies: The H<scp>i</scp>Mass Function and_{H<scp>i</scp>}

Abstract

We present a new accurate measurement of the HI mass function of galaxies\nfrom the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the\nhighest HI peak flux densities in the southern hemisphere (Koribalski et al.\n2003). This sample spans nearly four orders of magnitude in HI mass (from log\nM_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected\ngalaxies to date. We develop a bivariate maximum likelihood technique to\nmeasure the space density of galaxies, and show that this is a robust method,\ninsensitive to the effects of large scale structure. The resulting HI mass\nfunction can be fitted satisfactorily with a Schechter function with faint-end\nslope alpha=-1.30. This slope is found to be dependent on morphological type,\nwith later type galaxies giving steeper slopes. We extensively test various\neffects that potentially bias the determination of the HI mass function,\nincluding peculiar motions of galaxies, large scale structure, selection bias,\nand inclination effects, and quantify these biases. The large sample of\ngalaxies enables an accurate measurement of the cosmological mass density of\nneutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies\ncontribute only 15% to this value, consistent with previous findings.\n