Mean Surface Density and Morphological Type in Disk Galaxies

Abstract

In Prieto et al. (1989), we have represented the rotational velocity, V, at a radius corresponding to 25 mag/arcsec² against this radius, R, for a sample of 56 spiral galaxies. We found that galaxies with different morphological types appear in different regions on this diagram, with some overlap between Sb and Sc. In the V-R diagram, we have plotted contours of total mass, angular momentum and “mean surface density” for a simple model of an isolated galaxy, considered as a disc with circular motion, in centrifugal equilibrium, showing that, up to a critical mass, “the mean surface density” or its observational parameter V²/R can represent the morphological type, independent of the mass. We found too that, for a constant mass, galaxies with different angular momentum are of a different type, such that those with smaller angular momentum are later types.