2006MNRAS.371..695C

We present deep radio observations of the most distant complete quasar sample drawn from the Sloan Digital Sky Survey. Combining our new data with those from literature, we obtain a sample which is ∼100 per cent complete down to S_1.4GHz= 60µJy over the redshift range 3.8 ≤ z ≤ 5. The fraction of radio detections is relatively high (∼43 per cent), similar to what observed locally in bright optical surveys. Even though the combined radio and optical properties of quasars remain overall unchanged from z ∼ 5 to the local Universe, there is some evidence for a slight overabundance of radio-loud (RL) sources at the highest redshifts when compared with the lower-z regime.

Exploiting the deep radio Very Large Array observations, we present the first attempt to directly derive the radio luminosity function of bright quasars at z ≳ 4. The unique depth - both in radio and optical - allows us to thoroughly explore the population of optically bright Fanaroff-Riley type II (FR II) quasars up to z ∼ 5 and opens a window on the behaviour of the brightest FR I sources. A close investigation of the space density of RL quasars also suggests a differential evolution, with the more luminous sources showing a less-pronounced cut-off at high z when compared with the less-luminous ones.