COLORS, LUMINOSITIES, AND MASSES OF DISK GALAXIES .2. ENVIRONMENTAL DEPENDENCIES

The B-band and near-infrared (H) luminosity functions of spiral galaxies are derived for the Coma and A1367 clusters and for a reference population of ''field'' galaxies in the Coma supercluster. They are consistent at the bright end, but they differ significantly at the faint end, indicating an overdensity of spirals with blue color (B-H < 3.0) and faint H luminosity (H > -21.5) in clusters with respect to the field. These objects have disturbed morphology and peculiar velocities significantly larger than the rest of the cluster sample. We discuss these results in the framework of a possible environmental dependence of galaxy evolution, and we conclude that enhanced current star formation in cluster spiral galaxies might occur due to molecular gas collapse stimulated by the ram-pressure mechanism.