The Nature and Observability of Protogalaxies

Abstract

I discuss recent theoretical work on the formation and evolution of galaxies paying particular attention to the ability of current models to make detailed comparisons with observations of the galaxy population both nearby and at high redshift. These models suggest that much (perhaps most) star formation in the universe took place in objects that are already detected in deep galaxy samples. In addition, they predict that systems with large star formation rates are unlikely to be much more abundant in the past than they are at present. Recent data show that the star formation rate in the nearby universe is, in fact, a substantial fraction of that required to make all the stars seen in galaxies, and that the observed abundance of objects forming stars at rates in excess of 10 solar masses per yr is approximately the same at redshifts of 1.25 and 3.25 as it is at z = 0. Both the epoch of galaxy formation and ``typical'' protogalaxies may already have been observed but not recognised. Thermal emission from dust in such protogalaxies could be detected by a large millimeter array, and molecular line observations could explore the dynamical state of the gas in the more massive systems.