Starbursts triggered by central overpressure in interacting galaxies

Abstract

We present a triggering mechanism for starbursts in the central regions of interacting galaxies. As a disk giant molecular cloud (GMC) falls into the central region of a galaxy following a galaxy encounter, it may be compressed by the high pressure of the inter-cloud medium. For a high enough pressure difference, the compression develops into an inwardly propagating, isothermal, spherical shock. When the growth time for gravitational instabilities in the shell become smaller than the crossing time of the shell, the shell becomes unstable and begins to fragment. This gives rise to a burst of star formation. For a galaxy with pre-counter gas parameters as in the Galaxy, this mechanism yields a lower limit to the infra-red luminosity of L approximately 2-6 × 10⁹ solar luminosity. For strong interactions or mergers L_IR less than or = 10¹² solar luminosity (Jog & Das 1992).