The Redshift Cutoff and the Quasar Epoch

We have obtained complete redshift information for a sample of 442 radio-loud quasars with flux densities S 11 ≥ 0.25 Jy. These come from a completely-identified sample of 878 flat-spectrum radio sources, so there is no optical magnitude limit. With these quasars, therefore, we can map out the entire quasar epoch, unhindered by optical selection effects and any intervening dust. The rapid decline in true space density above z ∼ 2.5 is confirmed. It agrees closely with that obtained from optically-selected samples, indicating that these are also not significantly affected by dust. The evolution of the quasar space density is similar to that deduced for the global star formation rate, implying that the quasar epoch may also be that of star formation. This sample of radio-selected quasars can now be used in a variety of other studies, including unbiased searches for damped Lyα absorbers, studies of the phenomenon of " red quasars " , and searches for high-redshift molecular absorption systems.