Identification of Two z ~ 3.8 QSOs in a Deep CCD Survey

We present the identifications of two z ~ 3.8 quasars from a deep UBI imaging survey with the Palomar 5.1 m Telescope. The survey covers an area of 0.25 degree² around a sample of ten z =0.2-0.3 luminous X-ray clusters. The QSOs were identified on the basis of their stellar morphologies, relatively blue optical and very red UV-optical colours. The two objects are Q 1322+5034, with total magnitudes of B =20.8, I =18.3 and (U-B) > 4.7, and Q 1722+3211, which has total magnitudes of B =21.8, I =19.7 and (U-B) > 3.2. Subsequent spectroscopic observations with the 4.2 m William Herschel Telescope have confirmed the identity of these two sources as QSOs at z =3.82 and z =3.73 respectively. Our spectroscopic observations identify a damped Lyman-α absorber in the spectrum of Q 1322+5034 at z =3.439, as well as a second absorption system at z =2.700, which may be either a single very high column density, damped Lyman-α system, or more likely a blend of a number of high column-density absorbers spread over a distance of ~10 Mpc.