EDP Sciences
Free access
Volume 391, Number 2, August IV 2002
Page(s) 509 - 517
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20020869

A&A 391, 509-517 (2002)
DOI: 10.1051/0004-6361:20020869

Discovery of radio-loud quasars with redshifts above 4 from the PMN sample

I. M. Hook1, R. G. McMahon2, P. A. Shaver3 and I. A. G. Snellen4

1  Department of Physics, University of Oxford, Nuclear & Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK
    e-mail: imh@astro.ox.ac.uk
2  Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
3  European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching b. München, Germany
4  Institute for Astronomy, Royal Observatory, Edinburgh, EH9 3HJ, UK

(Received 5 February 2002 / Accepted 11 June 2002 )

We present results of a new, large survey for high-redshift radio-loud quasars, which targets quasars with z>4. The survey is based on the PMN and NVSS radio surveys, optically identified using digitised UKST B, R and I plates. Six new z>4 flat-spectrum QSOs have been discovered, and one previously known z>4 QSO rediscovered, based on their red optical colours. The QSOs discovered in this survey are bright in both radio and optical bands; in particular PMN J1451-1512 ( z=4.763, $\rm I=17.3$, R=19.1) and PMN J0324-2918 ( z=4.630, R=18.7) are very luminous. PMN J1451-1512 at z=4.763 is also now the most distant radio-selected quasar. In addition, 9 new quasars with 3.5<z<4.0 were discovered during the survey. We present spectra and finding charts for the new quasars. We also derive a surface density of $\rm 1.0\pm 0.4\times 10^{-3} ~sq\ deg^{-1}$ for flat-spectrum z>4 QSOs with $S\ge 72$ mJy and $\it R < 21$ mag.

Key words: quasars: general

Offprint request: I. M. Hook, ihook@gemini.edu

© ESO 2002