SIMBAD references

In this paper, we collect radio and X-ray observations for most Fanaroff-Riley I (FR I) radio galaxies in the Zirbel-Baum radio galaxy sample and investigate the distribution of the radio-to-X-ray effective spectral index, α_rx, to test the unified scheme of BL Lac objects and FR I radio galaxies. It is found that the range of α_rx for FR I radio galaxies is almost the same as that for BL Lac objects, that the distribution of α_rx probably peaks at the same position as BL Lac objects, and that the distribution of α_rx for FR I galaxies is similar to that for BL Lac objects. These suggest that there exist two subclasses of FR I 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 is consistent with previous VLA observations and supports the unified scheme of BL Lac objects and FR I radio galaxies.