The Deep X-Ray Radio Blazar Survey (DXRBS). III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars

摘要

Our knowledge of the blazar surface densities and luminosity functions, whichare fundamental parameters, relies still on samples at relatively high fluxlimits. As a result, our understanding of this rare class of active galacticnuclei is mostly based on relatively bright and intrinsically luminous sources.We present the radio number counts, evolutionary properties, and luminosityfunctions of the faintest blazar sample with basically complete (~ 95%)identifications. Based on the Deep X-ray Radio Blazar Survey (DXRBS), itincludes 129 flat-spectrum radio quasars (FSRQ) and 24 BL Lacs down to a 5 GHzflux and power ~ 50 mJy and ~ 10^{24} W/Hz, respectively, an order of magnitudeimprovement as compared to previously published (radio-selected) blazarsamples. DXRBS FSRQ are seen to evolve strongly, up to redshift ~ 1.5, abovewhich high-power sources show a decline in their comoving space density. DXRBSBL Lacs, on the other hand, do not evolve. High-energy (HBL) and low-energy(LBL) peaked BL Lacs share the same lack of cosmological evolution, which is atvariance with some previous results. The observed luminosity functions are ingood agreement with the predictions of unified schemes, with FSRQ getting closeto their expected minimum power. Despite the fact that the large majority ofour blazars are FSRQ, BL Lacs are intrinsically ~ 50 times more numerous.Finally, the relative numbers of HBL and LBL in the radio and X-ray bands aredifferent from those predicted by the so-called "blazar sequence" and support ascenario in which HBL represent a small minority (~ 10%) of all BL Lacs.