Self-consistent Models of Spherical Galaxies with Dark Matter

Abstract

A well-known result of the analysis of extended HI rotation curves of spiral galaxies is that these objects have an M/L ratio that increases with the galactocentric distance. For the case of elliptical galaxies, for an approximately constant M/L ratio, the rotation curve of a disk of gas, if present in the galaxy, would show a keplerian decrease beyond the half luminosity radius R e . In addition, the stellar velocity dispersion profile projected along the line of sight σ p (R) would also be rapidly decreasing with the distance (for a wide class of models where pressure anisotropy is the one suggested by numerical experiments of galaxy formation (van Albada 1982) and mean motions of the stars are dynamically insignificant). Therefore evidence for the presence of a dark component in elliptical galaxies, distributed differently from the luminous matter, could be obtained if new kinematical data on a larger radial extent will show that σ p is only slowly decreasing (Bertin et al. 1989), thereby confirming the indications deriving from the observations of the few ellipticals that possess a gaseous disk (see the flat HI rotation curves measured by Raimond et al. 1981 and by Schweizer, van Gorkom, and Seitzer 1989).