A search for distant radio-loud quasars in the CLASS survey: three new radio-selected quasars at z > 4 |
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| Authors: | IAG Snellen RG McMahon J Dennett-Thorpe N Jackson K-H Mack E Xanthopoulos |
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| Institution: | ;1Institute of Astronomy, Madingley Road, Cambridge CB3 0HA2Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ;3Kapteyn Institute, Rijksuniversiteit Groningen, 9700 AV Groningen, the Netherlands;4Jodrell Bank Observatory, University of Manchester, Macclesfield, Cheshire SK11 9DL;5Istituto di Radioastronomia de CNR, Via Gobetti 101, I-40129 Bologna, Italy;6Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany;7ASTRON, PO Box 2, 7990 AA Dwingeloo, the Netherlands |
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| Abstract: | We report on the search for distant radio-loud quasars in the Cosmic Lens All Sky Survey (CLASS) of flat spectrum radio sources with S 5GHz>30 mJy . Unresolved optical counterparts were selected from APM scans of POSS-I plates, with e <19.0 and red o ? e >2.0 colours, in an effective area of ～6400 deg2. Four sources were found to be quasars with z >4 , of which one was previously known. This sample bridges the gap between the strong radio surveys with S 5GHz>200 mJy and the samples of radio-weak quasars that can be generated via radio observations of optically selected quasars. In addition, four new quasars at z >3 have been found. The selection criteria result in a success-rate of ～1:7 for radio-loud quasars at z >4 , which is a significant improvement over previous studies. This search yields a surface density of 1 per 1600 deg2, which is about a factor of ～15 lower than that found in a similar search for radio-quiet quasars at z >4 . The study presented here is strongly biased against quasars beyond z >4.5 , since the e -passband of the POSS-I only samples the spectra shortward of 1200 Å at these redshifts. |
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| Keywords: | surveys quasars: general radio continuum: galaxies |
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