STARBURSTS BY GRAVITATIONAL COLLAPSE IN THE INNER LINDBLAD RESONANCE RINGS OF GALAXIES

Starbursts in inner Lindblad resonance rings are proposed to result fr om gravitational instabilities that fragment the ring into several bou nd clouds. Each cloud forms a separate star cluster or hot spot after further energy dissipation and collapse. A linear instability analysis including accretion and an azimuthal magnetic field suggests that the ring instability occurs only after a critical density is reached, whi ch presumably follows a relatively long epoch of gas accretion from ba r or spiral torques. The critical density is very high in the inner re gions because the Coriolis and tidal forces are high. Typical densitie s are > 100 cm(-3), depending on the inner Lindblad resonance radius, rotation curve, accretion rate, and other parameters. The rapid star f ormation in the starburst follows from the high density at the expecte d rate epsilon omega rho for local efficiency per cloud epsilon, insta bility growth rate omega, and density rho. Most of the high rate comes from the density dependence of omega(rho)rho, but the efficiency epsi lon could also increase if the ambient velocity dispersion is high in the ring.