Dynamical properties and two-dimensional classification of disk galaxies

We try to classify disk galaxies in terms of their dynamical characteristics alone. Examining twenty-two disk galaxies whose rotation curves are well determined, we find that disk galaxies can be classified two-dimensionally in terms of k (=V2 sub(max)/r sub(max)) and M (mass of galaxy), where k is the centrifugal force at the radius r sub(max) at which rotational velocity attains its maximum value V sub(max). The quantity k is found to be correlated with morphological types and to be an indicator for the mass ratio of the bulge to the disk. On the other hand, k is not correlated with M, and thus the mass is the other quantity to specify disk galaxies. The parameter beta=R sub(Hol)/r sub(max), where R sub(Hol) is Holmberg's (1958) optical radius of galaxies, has correlations with k or morphological types. The analysis of mass distributions, calculated from a truncated Brandt and Belton's (1962) mass model described here, reveals that beta is an indicator of the relative importance of the bulge to the disk. Calculations of representative values of angular momentum beta and rotational energy T by this mass model show that for a given morphological type, the relations Q proportional to Msup(7/4) and T proportional to Msup(3/2) hold. The proportional coefficients in these relations change by morphological types such that latetype galaxies have systematically larger angular momenta and smaller rotational energies than early-type galaxies of the same masses have. (auth.)