The Evolution of Galaxies and Active Galaxies with Cosmic Epoch

Abstract

Evidence for strong evolutionary changes of the populations of extragalactic objects with cosmic epoch was first found in surveys of extragalactic radio sources and quasars in the 1950s and 1960s. An excess of faint sources was discovered in radio source and quasar surveys as compared with the expectations of uniform world models. The inference was that these classes of objects were much more common at earlier cosmic epochs than they are at the present time. During the 1980s, the first deep counts of galaxies to very faint magnitudes became available thanks to the CCD revolution in optical detector technology. An excess of faint blue galaxies was discovered at faint apparent magnitudes and these studies were extended to extremely faint galaxies by Hubble Space Telescope observations of the Hubble Deep Field and the Hubble Ultra Deep Field