On the Absence of Core Luminosity–Core-Dominance Parameter (PC – R) Correlation in Radio Galaxies and BL Lacs

Abstract

We have presented an alternative interpretation for the absence of correlation in the relationship between the core radio power (PC) and core-dominance parameter (R) for a sample of BL Lacs and radio galaxies found in Fan & Zhang (Astron. Astrophys. 407, 89 (2003)). This is contrary to the predictions of the relativistic beaming and radio source orientation models in which the core luminosity is expected to be Doppler-boosted relative to the extended luminosity which is generally assumed to be isotropic. Our analysis of the PC − R data indicates a strong luminosity selection effect (reminiscent of bright source samples due to Malmquist bias) in the sample. In particular, we showed that a strong PC − R correlation exists above some redshift cut-off which may correspond to the flux limit of the sample used.