Young galaxies, quasars and the cosmological evolution of extragalactic radio sources

The V/Vsub(max) test for quasars and the counts of radio sources show that the most powerful extragalactic radio sources exhibit strong evolutionary changes with cosmological epoch. The bulk of the evolution occurs within the range of observationally accessible redshifts. These evolutionary changes are empirical results derived from observation but there has been little interpretation of their cosmological significance. This is because neither the theory of the origin and evolution of galaxies nor that of radio sources is in a state where it can account for the properties at a single epoch, let alone how they might change with time. Nontheless, speculation about the significance of these results may be used if it suggests potentially fruitful lines of observational and theoretical investigations. (Auth.)