Luminosity Selection Effects and Linear Size Evolution in the Quasar/Galaxy Unification Scheme

Abstract

The implications of linear size evolution and luminosity selection effects in the quasar/galaxy unification scheme have been investigated. We show that both radio galaxies and quasars undergo similar size evolution above some low redshift cut-off z_c = 0·2–0·3. However, this evolution can be attributed largely to the strong luminosity selection effects present in the sample. We also observe that there is a marked difference in the luminosity–redshift slope between low and high redshift sources, which may be responsible for the conflicting results in the literature as to whether or not radio galaxies and quasars have similar linear size versus luminosity/redshift relationships. Our present result seems consistent with the quasar/galaxy unification scheme in which the two classes of object are expected to have similar linear size versus luminosity/redshift relationships.