| Abstract | Tight correlations are found between blue-to-IR colors and either the H I line profile widths (masses) or the intrinsic luminosities of spiral galaxies. Since colors are distance independent, the color-magnitude correlation can be used as a measuring stick. The tight relationships between color and mass or luminosity, essentially independent of galaxy type, suggest that the Hubble morphological sequence is predominantly dependent on a single parameter: total mass. The color-magnitude diagram can be qualitatively understood if the initial specific star formation rate in spirals decreases with decreasing mass, and at the same time, chemical abundances decrease and/or the initial mass function flattens with decreasing mass. It is suggested that a gas-rich galaxy will lie on the spiral branch at a location specified by its total mass, and, once its gas is depleted or lost, will rapidly evolve to a location on the lenticular branch that is specified by the total mass. |
