Starbursts by gravitational collapse in the inner Lindblad resonance rings of galaxies

Abstract

Starbursts in inner Lindblad resonance rings are proposed to result from gravitational instabilities that fragment the ring into several bound 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, which presumably follows a relatively long epoch of gas accretion from bar or spiral torques. The critical density is very high in the inner regions because the Coriolis and tidal forces are high. Typical densities are > 100 cm-3, depending on the inner Lindblad resonance radius, rotation curve, accretion rate, and other parameters. The rapid star formation in the starburst follows from the high density at the expected rate ∈ωρ for local efficiency per cloud ∈, instability growth rate ω, and density ρ. Most of the high rate comes from the density dependence of ω(ρ)ρ, but the efficiency ∈ could also increase if the ambient velocity dispersion is high in the ring.