The 1.4 gigahertz luminosity function and its evolution

The local luminosity function was determined at v = 1.4 GHz from radio observations of two low-redshift galaxy samples: (1) spiral and irregular galaxies with apparent blue magnitudes B_T_ <= + 12 and declinations δ >= -45^deg^ and (2) galaxies of all morphologies with blue angular diameters θ_M_ >= 1.0' in the declination range -2.5^deg^ <= δ <= +82^deg^. Separate luminosity functions for the radio source populations powered by "starbursts" and "monsters" were obtained from the latter sample. Locally these two energy sources contribute almost equally to the 1.4 GHz spectral power density (U ~ 2 x 10^19^ W Hz^-1^ Mpc^-3^ and U ~ 3 x 10^19^ W Hz^-1^ Mpc^-3^, respectively, for H_0_ = 50 km s^-1^ Mpc^-1^). The new luminosity functions and the counts of faint (S <= 1 mJy) radio sources found at v = 1.4 GHz together imply strong cosmological evolution of sources fainter than L ~ 10^24^ W Hz^-1^. This evolution is so strong that most features of the observed radio source counts and redshift distributions can be explained by a remarkably simple evolutionary model that places all radio sources in a hollow spherical shell at z ~ 0.8.