The Nature of Starburst Galaxies

Utilizing a large sample of infrared-selected starburst galaxies having optical images and long-slit spectra, we explore the interrelationships between the properties of starbursts and relate these properties to those of the "" host galaxy. We nd that the half-light radius of the Ha-emitting region enters (r e, Ha) into several correlations that suggest it is physically related to the actual starburst radius. Most suggestively, the e ective IR surface brightness correlates strongly with the far-IR color temperature. (L IR /nr e, Ha 2) This can be reproduced roughly with an idealized model of a surrounding dust screen whose far-IR emissivity is determined by the local energy density of UV starburst light. Typical values for are a r e, Ha few hundred pc to a few kpc (with the Ha emission being signicantly more compact than the red starlight). This conrms the "" circumnuclear scales of typical starbursts. We show also that starbursts seem to obey a limiting IR surface brightness of about 1011 kpc2, corresponding to a maximum star L _ formation rate of about 20 yr~1 kpc2 for a normal initial mass function. We argue that this upper M _ limit suggests that starbursts are self-regulating in some way.