On the Radio and Optical Luminosity Evolution of Quasars
  We calculate simultaneously the radio and optical luminosity evolutions of
quasars, and the distribution in radio loudness R defined as the ratio of radio
and optical luminosities, using a flux limited data set containing 636 quasars
with radio and optical fluxes from White et al. We first note that when dealing
with multivariate data it is imperative to first determine the true
correlations among the variables, not those introduced by the observational
selection effects, before obtaining the individual distributions of the
variables. We use the methods developed by Efron and Petrosian which are
designed to obtain unbiased correlations, distributions, and evolution with
redshift from a data set truncated due to observational biases. It is found
that the population of quasars exhibits strong positive correlation between the
radio and optical luminosities. With this correlation, whether intrinsic or
observationally induced accounted for, we find that there is a strong
luminosity evolution with redshift in both wavebands, with significantly higher
radio than optical evolution. We also construct the local radio and optical
luminosity functions and the density evolution. Finally, we consider the
distribution of the radio loudness parameter R obtained from careful treatment
of the selection effects and luminosity evolutions with that obtained from the
raw data without such considerations. We find a significant difference between
the two distributions and no clear sign of bi-modality in the true distribution
for the range of R values considered. Our results indicate therefore, somewhat
surprisingly, that there is no critical switch in the efficiency of the
production of disk outflows/jets between very radio quiet and very radio loud
quasars, but rather a smooth transition. Also, this efficiency seems higher for
the high-redshift and more luminous sources in the considered sample.
