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

Abstract

We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3 ¹ z ¹ 1.5 and an optical absolute magni-tude range of (h \ 1/2, We have also matched other existing surveys [26.5 ¹ M B ¹ [23.5 q 0 \ 1/2). with the Faint Images of the Radio Sky at Twenty Centimeters and NRAO VLA Sky Survey radio catalogs and combined these data so that the optical luminosityÈredshift plane is now far better sampled than before. We have Ðtted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift, and from this model we infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and Ñatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the di erence in the rate of evolutions of the two di erent classes is much less than was previously thought. We show, using Monte Carlo simulations, that the observed di erence in the shape of the optical luminosity func-tions can be partly accounted for by Doppler boosting of the optical continuum of the radio-loud quasars, and we explain how this can be tested in the future.