Comparisons of Jet Properties between GeV Radio Galaxies and Blazars

Abstract

We compile a sample of spectral energy distribution (SED) of 12 GeV radio galaxies (RGs), including eight FR I RGs and four FR II RGs. These SEDs can be represented with the one-zone leptonic model. No significant unification as expected in the unification model is found for the derived jet parameters between FR I RGs and BL Lacertae objects (BL Lacs) and between FR II RGs and flat spectrum radio quasars (FSRQs). However, on average FR I RGs have the larger gamma_b (break Lorentz factor of electrons) and lower B (magnetic field strength) than FR II RGs, analogous to the differences between BL Lacs and FSRQs. The derived Doppler factors (delta) of RGs are on average smaller than that of balzars, which is consistent with the unification model that RGs are the misaligned parent populations of blazars with smaller delta. On the basis of jet parameters from SED fits, we calculate their jet powers and the powers carried by each component, and compare their jet compositions and radiation efficiencies with blazars. Most of the RG jets may be dominated by particles, like BL Lacs, not FSRQs. However, the jets of RGs with higher radiation efficiencies tend to have higher jet magnetization. A strong anticorrelation between synchrotron peak frequency and jet power is observed for the GeV RGs and blazars in both the observer and co-moving frames, indicating that the "sequence" behavior among blazars, together with the GeV RGs, may be dominated by the jet power intrinsically.