Luminosity as a function of redshift for sources with flux density S​_1.4 GHz = 6.1 mJy (solid line), 17.1 mJy (dotted line), and 169.7 mJy (dashed line). These correspond to the faintest source with an unknown redshift in the sample, the faintest source with an unknown redshift studied in this paper, and the brightest source of the sample with an unknown redshift, respectively. Stars are sources with known redshifts.