EFFECTS OF GAS ON THE GLOBAL STABILITY OF GALACTIC DISKS - RADIAL FLOWS

We study numerically the effect of gas on the global stability of a tw o-component self-gravitating galactic disk embedded in a live halo. Th e stars are evolved by using a three-dimensional collisionless N-body code, and the gas is represented by an ensemble of finite size inelast ic particles. The gravitational interaction of stars and gas is calcul ated using a TREE method. We find that the evolution of the gaseous di stribution in the globally unstable disks can be described by two diff erent regimes. When the gas mass fraction is less than approximately 1 0%, the gas is channeled toward the galactic center by a growing stell ar bar. For higher gas fractions, the gas becomes highly inhomogeneous , and the bar instability in the disk is heavily damped. The gas falls toward the inner kpc due to dynamical friction. Domains of both regim es depend on the efficiency of dissipation in the gas. We also discuss the relevance of the Jeans instability and give an empirical criterio n for the global bar instability in a two-component self-gravitating d isk.