Cosmological evolution of compact AGN at 15 GHz

Abstract

We study the uniformity of the distribution of compact flat-spectrum AGN on the sky and the evolution of their relativistic jets with cosmic epoch. A complete sample of compact extragalactic radio sources at 15 GHz was recently compiled to conduct the MOJAVE program. The MOJAVE sample comprises 133 radio-loud flat-spectrum AGN with compact relativistic outflows detected at parsec scales. The source counts of compact AGN shows that the MOJAVE sample represents a flux-limited complete sample. Analysis of the population of flat-spectrum quasars of the sample reveals that the pc-scale jets of quasars have intrinsic luminosities in the range between ~10^24 W/Hz and ~10^27 W/Hz and Lorentz factors distributed between 3 and 30. We find that the apparent speed (or Lorentz factor) of jets evolves with redshift, increasing from z~0 to z~1 and then falling at higher redshifts (z~2.5) by a factor of 2.5. The evolution of apparent speeds does not affect significantly the evolution of the beamed luminosity function of quasars, which is most likely to be dependent on the evolution of radio luminosity. Furthermore, the beamed radio luminosity function suggests that the intrinsic luminosity function of quasars has a double power-law form: it is flat at low luminosities and steep at high luminosities. There is a positive evolution of quasars at low redshifts (z 1.7 with space density decline up to z~2.5. This implies that the powerful jets were more populous at redshifts between 0.5 and 1.7. We show that the evolution of compact quasars is luminosity dependent and it depends strongly on the speed of the jet suggesting that there are two distinct populations of quasars with slow and fast jets which evolve differently with redshift.