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

Abstract

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 J 1451-1512 (z = 4,763, 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 1.0 ± 0.4 × 10-3 sq deg-1 for flat-spectrum z > 4 QSOs with S ≥ 72 mJy and R < 21 mag.