Dissipative models of spiral galaxies

Abstract

Self-consistent A/-body experiments have been performed for a galactic disk containing both stars and a dissipative gas component. The gas is treated with a simple sticky particle scheme, which maintains the gas at a low velocity dispersion and results in continuous dynamical cooling of the disk. The disks exhibit dramatic activity, with both the stars and the gas showing large-scale spiral structure. The gas arms generally overlie the stellar arms but are much narrower and show structure on smaller scales than the stars. The number of spiral arms m is found to be strongly correlated with the fraction of the total mass in the disk /, such that m is approximately equal to 1//, as expected from swing amplification theory. A population of disk stars with a large velocity dispersion (Q » 2.5) is shown to be so "stiff" that it is effectively in the halo, as far as spiral activity is concerned. The gas loses angular momentum to the stars, resulting in a slow inward radial flow on a time scale of about 100 revolutions.