Correlation of the dark mass in galaxies with Hubble type

Abstract

The slow increase of M/L with colour for spiral galaxies shows that the mass ratio of dark material to ordinary stars is greater in blue galaxies than in red ones; the masses referred to are those within the Holmberg radii of the galaxies. Two possible interpretations of this result are that bluer galaxies form stars with an initial mass function weighted toward low stellar masses, or that bluer galaxies have relatively more massive dark haloes. The latter hypothesis is supported by the much faster increase of M/L with radius in late- than in early-type galaxies, and by the need for a dark halo to stabilize the discs of late-type spirals. The relative dominance of dark haloes in late-type galaxies is explained tentatively, in the context of current models for galaxy formation.