The Deep X-Ray Radio Blazar Survey (DXRBS). III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars
Padovani, P. ; Giommi, P. ; Landt, H. ; et al.
Jan - 2007
DOI: 10.1086/516815

journal : PREPRINT
type: Article Journal

Abstract
Our knowledge of the blazar surface densities and luminosity functions, which are fundamental parameters, relies still on samples at relatively high flux limits. As a result, our understanding of this rare class of active galactic nuclei is mostly based on relatively bright and intrinsically luminous sources. We present the radio number counts, evolutionary properties, and luminosity functions of the faintest blazar sample with basically complete ( 95\%) identifications. Based on the Deep X-ray Radio Blazar Survey (DXRBS), it includes 129 flat-spectrum radio quasars (FSRQ) and 24 BL Lacs down to a 5 GHz flux and power 50 mJy and 10\^\24\ W/Hz, respectively, an order of magnitude improvement as compared to previously published (radio-selected) blazar samples. DXRBS FSRQ are seen to evolve strongly, up to redshift 1.5, above which high-power sources show a decline in their comoving space density. DXRBS BL 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 at variance with some previous results. The observed luminosity functions are in good agreement with the predictions of unified schemes, with FSRQ getting close to their expected minimum power. Despite the fact that the large majority of our 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 are different from those predicted by the so-called blazar sequence and support a scenario in which HBL represent a small minority ( 10\%) of all BL Lacs.

keywords : Astrophysics