Cosmological evolution of radio sources

Abstract

Data which encompass source counts at five different frequencies, together with redshift distributions of strong sources, spectral index distributions of sources, and the 1.4-GHz local luminosity function, are presently used to constrain the epoch-dependent spectral luminosity function of extragalactic radio sources. A simple evolutionary model is found for the spectral luminosity function which is consistent with these data, as well as the magnitude distribution of galaxies optically identified with faint sources, and with in addition evolves all sources in the same way. This last feature renders the model consistent with physical mechanisms of evolution which do not distinguish between low luminosity and high luminosity sources. The model suggests that the question as to whether the mean spectral index of steep spectrum sources correlates with luminosity or redshift may be decidable on the basis of the spectral index distributions of faint sources, even if no redshifts are available for them.