THE EVOLUTION OF THE DISTRIBUTION OF STAR-FORMATION RATES IN GALAXIES

A large, deep, and nearly complete B < 24.5 redshift sample is used to measure the change with redshift in the distribution function of the stellar mass production rate in individual galaxies. The evolution of the star formation rate distribution with redshift is interpreted in t erms of the history of spiral galaxy formation, with the disk componen t modeled as a single evolving entity, and the characteristic timescal es, luminosities, and epochs varying according to galaxy type. The mor e massive forming galaxies seen at z = 1-3 are identified as earlier t ype spirals, whose star formation rates are initially high and then de cline rapidly at z < 1, while for later type spirals and smaller mass irregulars the mass formation rates at z < 1 are lower, and the format ion process persists to redshifts much closer to the present epoch. We find that these models can be consistent with the data and fit well i nto a broad picture of other recent results if q(0) = 0.02 and many of the disks begin their growth at z much less than 3, but that they pre dict too many bright star formers at high z in flat universes.