Recent star formation in interacting galaxies - II. Super starbursts in merging galaxies

Abstract

The subset of galaxy-galaxy interactions which have resulted in a merger are, as a class, ultraluminous IR galaxies. Their IR luminosities span a narrow range which overlaps with the most luminous Seyfert galaxies. However, in contrast with Seyfert galaxies, the available optical, IR, and radio properties of mergers show no evidence for a compact nonthermal central source, and are easily understood in terms of a burst of star formation of extraordinary intensity and spatial extent; they are 'superstarbursts. It is argued that superstarbursts occur in the evolution of most mergers, and the implications of superstarbursts for the suggestion that mergers evolve into elliptical galaxies are discussed. Finally, it is noted that merger-induced shocks are likely to leave the gas from both galaxies in dense molecular form which will rapidly cool, collapse, and fragment. Thus a merger might in fact be expected to result in a burst of star formation of exceptional intensity and spatial extent, i. e., a superstarburst.