Radio core-dominance of Fermi-blazars: implication for blazar unification

Abstract

In this paper, we use the distributions of two-component radio emissions to investigate the consequences of relativistic beaming on the unified scheme of blazar populations and radio galaxies. Our results show remarkable continuity in the distributions of source luminosities (radio core and extended luminosities, $L_{C}$ and $L_{E}$ respectively as well as $\gamma$-ray luminosity $L_{\gamma }$) from radio galaxies at low luminosities to FSRQs at high luminosities through BL subclasses as expected in the blazar unification scheme in a sense suggesting that the sequence of BL Lacs, FSRQs and radio galaxies represents progressively misaligned populations of AGNs. Distribution of radio core-dominance is consistent with average projection angles of 13.5^∘, 14.8^∘, 16.8^∘, 20.4^∘ and 28.2^∘ for ISPs, LSPs, FSRQs, HSPs, and radio galaxies, respectively. Linear regression analyses of our data yield significant anti-correlation ($r > 0.60$) between core-dominance parameter ($C$) and $L_{E}$ in each individual subsample: the correlation is significant only when individual subsamples are considered. There is a systematic sequence of the distribution of the different subclasses on the $C - L_{E}$ plane. Nevertheless, little or no correlation between $C$ and $L_{C}$ or between $C$ and $L_{\gamma }$ ($r < 0.50$) was observed. There is a clear dichotomy between high synchrotron-peaking BL Lacs and other BL Lac subclasses. The results are consistent with a unified view for blazars and can be understood in terms of relativistic beaming persisting at largest scales.