The Parkes quarter-Jansky flat-spectrum sample - 2. New optical spectra and redshift measurements

We present optical spectra and redshift measurements for 178 flat-spectrum objects from the Parkes quarter-Jansky flat-spectrum sample. These spectra were obtained in order to compile a complete sample of quasars for use in a study of quasar evolution. We present a composite optical spectrum made from the subset of 109 quasars that have flux densities in the range 0.25 Jy < S-2.7 (GHz) < 0.5 Jy, and make a comparison with a composite for radio-quiet QSOs from the Large Bright Quasar Survey. Our large sample of radio-loud quasars allows us to strengthen previous reports that the Lyalpha and CIV emission lines have larger equivalent width in radio-loud quasars than radio-quiet QSOs to greater than the 3sigma level. However we see no significant difference in the equivalent widths of CIII] or MgII. We also show that the flux decrements across the Lyman-alpha line (D-A) measured from these spectra show the same trend with redshift as for optically selected QSOs.