THE HI content of local late-type galaxies

We present a solid relationship between the neutral hydrogen (H I) disk mass and the stellar disk mass of late-type galaxies in the local universe. This relationship is derived by comparing the stellar disk mass function from the Sloan Digital Sky Survey and the H I mass function from the H I Parkes All Sky Survey (HIPASS). We find that the H I mass in late-type galaxies tightly correlates with the stellar mass over three orders of magnitude in stellar disk mass. We cross-check our result with that obtained from a sample of HIPASS objects for which the stellar mass has been obtained by inner kinematics. In addition, we derive the H I versus halo mass relationship and the dependence of all the baryonic components in spirals on the host halo mass. These relationships bear the imprint of the processes ruling galaxy formation, and highlight the inefficiency of galaxies both in forming stars and in retaining their pristine Hi gas.