Evidence for the cosmological evolution of active galaxies

Investigations of the radial distribution of quasars and radio galaxies attest to a period of relatively violent activity at earlier epochs of the Universe. The evidence is from applications of the luminosity-volume (V/Vsub(max)) test, and from interpretations of source counts at both radio ('log N-log S' curve) and optical ('log N - m' curve) wavelengths. Here these techniques are discussed in the light of modern data. In addition to confirming the existence of powerful cosmic evolution, these data allow some detail of the evolution to be delineated, and indicate marked differences among the revolutionary behaviours of different populations of active galaxies. Some physical considerations are briefly described. (author)