New Evidence for the Unified Scheme of BL Lac Objects and Fri Radio Galaxies

摘要

In this paper, we collect radio and X-ray observations for mostFanaroff-Riley I (FRI) radio galaxies in the Zirbel-Baum radio galaxy sample,and investigate the distribution of the radio-to-X-ray effective spectralindex, $lpha_{rx}$, to test the unified scheme of BL Lac objects and FRIradio galaxies. It is found that the range of $lpha_{rx}$ for FRI radiogalaxies is almost the same as that for BL Lac objects, that the distributionof $lpha_{rx}$ probably peaks at the same position as BL Lac objects, andthat the distribution of $lpha_{rx}$ for FRIs is similar to that for BL Lacobjects. These suggest that there exist two subclasses of FRI radio galaxies:one is HBL-like, and the other is LBL-like, corresponding to high-energy-peaked(HBL) and low--energy-peaked (LBL) BL Lac objects, respectively. This result isconsistent with previous VLA observations, and supports the unified scheme ofBL Lac objects and FRI radio galaxies.