Gas and Galaxy Formation

Abstract

The theory of galaxy formation is reviewed brie°y. From the evidence of clusters today, the primordial gas fraction was 20% or more. Thus, while the Universe is dominated by dark matter, gas plays an appreciable role in galaxy formation. Collapses of dwarf protogalaxies produce predominantly cold gas. It is argued that, in such cold collapses, the collapsed gas is largely self-gravitating. As a result, gas processes play a critical role in determining the visible structure of galaxies.