High-redshift qsos in the FIRST survey

n a pilot search for high-redshift radio quasi-stellar objects (QSOs), we have obtained spectra of 55 FIRST sources (S1.4GHz>1mJy) with very red (O-E>3) starlike optical identifications. 10 of the candidates are QSOs with redshifts 3.64. The remaining 45 candidates comprise: one z=2.6 broad-absorption-line (BAL) QSO; three low-redshift galaxies with narrow emission lines; 18 probable radio galaxies; and 23 M stars (mainly misidentifications). The success rate (high-redshift QSOs / spectroscopically-observed candidates) for this search is 1/2 for S1.4GHz>10mJy, and 1/9 for S1.4GHz>1mJy. With an effective search area of 4030deg2, the surface density of high-redshift (z>4) QSOs discovered with this technique is 0.0015deg-2.