Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-06-13
Mon.Not.Roy.Astron.Soc.371:695-702,2006
Astronomy and Astrophysics
Astrophysics
Accepted for publication in MNRAS, 8 pages, 6 figures
Scientific paper
10.1111/j.1365-2966.2006.10695.x
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 = 60 \mu Jy 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 over-abundance of radio-loud sources at the highest redshifts when compared with the lower-z regime. Exploiting the deep radio VLA 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 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 radio loud 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.
Celotti Annalisa
Cirasuolo Michele
Cristiani Stefano
Danese Lugi
Gentile Gianfranco
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