Nature and evolution of powerful radio galaxies and their link with the
  quasar luminosity function
  Current wide-area radio surveys are dominated by active galactic nuclei, yet
many of these sources have no identified optical counterparts. Here we
investigate whether one can constrain the nature and properties of these
sources, using Fanaroff-Riley type II (FRII) radio galaxies as probes. These
sources are easy to identify since the angular separation of their lobes
remains almost constant at some tens of arcseconds for z>1. Using a simple
algorithm applied to the FIRST survey, we obtain the largest FRII sample to
date, containing over ten thousand double-lobed sources. A subset of 459
sources is matched to SDSS quasars. This sample yields a statistically
meaningful description of the fraction of quasars with lobes as a function of
redshift and luminosity. This relation is combined with the bolometric quasar
luminosity function, as derived from surveys at IR to hard X-ray frequencies,
and a disc-lobe correlation to obtain a robust prediction for the density of
FRIIs on the radio sky. We find that the observed density can be explained by
the population of known quasars, implying that the majority of powerful jets
originate from a radiatively efficient accretion flow with a linear jet-disc
coupling. Finally, we show that high-redshift jets are more often quenched
within 100 kpc, suggesting a higher efficiency of jet-induced feedback into
their host galaxies.
