DARK-MATTER IN SPIRAL HALOS AND THE HALO MASS FUNCTION

Evidence that low-luminosity spirals have a higher dark matter fractio n than their high-luminosity counterparts is discussed. The empirical correlation between dark matter fraction and luminosity is used, in co njunction with the galaxy luminosity function of spirals, to derive th e dark halo mass function of these galaxies. The mass function is show n to be consistent with hierarchical clustering models of galaxy forma tion. This contrasts with previous results based on the assumption of a constant mass-to-light ratio for all spirals, which predict too many low-luminosity galaxies.