The Parkes quarter-Jansky flat-spectrum sample 2. New Optical Spectra and Redshift Measurements

Abstract

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 0.25Jy < S(2.7GHz)< 0.5Jy, 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 Ly-alpha and CIV emission lines have larger equivalent width in radio-loud quasars than radio-quiet QSOs to greater than the 3-sigma 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.

20 pages, 8 figures. Accepted for publication in Astronomy and Astrophysics