A search for distant radio-loud quasars in the CLASS survey: three new radio-selected quasars at z>4

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 deg^2. 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, 4 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 deg^2, 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 Angstrom at these redshifts.

arXiv commentLaTeX, 7 pages, 5 Figs: to be published in MNRAS

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Cited by in corpus (13)

• The Cosmic Lens All-Sky Survey: I. Source selection and observations
• The FIRST-2MASS Red Quasar Survey II: An anomalously high fraction of LoBALs in searches for dust-reddened quasars
• The ESI/KeckII Damped Lya Abundance Database
• An X-ray jet discovered by Chandra in the z=4.3 radio-selected quasar GB 1508+5714
• Chandra Observations of Radio-Loud Quasars at z > 4: X-rays from the Radio Beacons of the Early Universe
• The space density of z>4 blazars
• Radio-Selected Quasars in the Sloan Digital Sky Survey
• X-ray spectral properties of high-redshift radio-loud quasars beyond redshift 4--first results
• Use of neural networks for the identification of new z>=3.6 QSOs from FIRST-SDSS DR5
• Decline of the space density of quasars between z=2 and z=4
• High-redshift QSOs in the FIRST survey
• A sample of radio-loud QSOs at redshift ~ 4
• A FIRST-APM-SDSS survey for high-redshift radio QSOs