A Comparison of the Optical Properties of Radio‐loud and Radio‐quiet Quasars

We have made radio observations of 87 optically selected quasars at 5 GHzwith the VLA in order to measure the radio power for these objects and hencedetermine how the fraction of radio-loud quasars varies with redshift andoptical luminosity. The sample has been selected from the recently completedEdinburgh Quasar Survey and covers a redshift range of 0.3 < z < 1.5 and anoptical absolute magnitude range of -26.5 < M_{B} < -23.5 (h, q_{0} = 1/2). Wehave also matched up other existing surveys with the FIRST and NVSS radiocatalogues and combined these data so that the optical luminosity-redshiftplane is now far better sampled than previously. We have fitted a model to theprobability of a quasar being radio-loud as a function of absolute magnitudeand redshift and from this model infer the radio-loud and radio-quiet opticalluminosity functions. The radio-loud optical luminosity function is featurelessand flatter than the radio-quiet one. It evolves at a marginally slower rate ifquasars evolve by density evolution, but the difference in the rate ofevolutions of the two different classes is much less than was previouslythought. We show, using Monte-Carlo simulations, that the observed differencein the shape of the optical luminosity functions can be partly accounted for byDoppler boosting of the optical continuum of the radio-loud quasars and explainhow this can be tested in the future.Comment: 33 pages, 9 postscript figures, uses the AAS aaspp4 LaTeX style file, to appear in the 1 February 1999 issue of The Astrophysical Journa