Do BL Lac Objects and FR I radiogalaxies inhabit the same galaxy environment?

Abstract

We investigate the environments of galaxies around BL Lac objects and FR I radiogalaxies, the alleged parent populations of misaligned sources. We compare the environment of a sample of 50 BL Lac objects at 0.1<z<0.33 with that of a sample of 90 FR I galaxies at 0.1<z< 0.15. The galaxy environment is estimated using the SDSS images in the i-band. We find that the galaxy excess density within 0.5 Mpc around of FR I radiogalaxies is a factor ~ 2 larger than that around BL Lacs. This implies a reconsideration of the parent population of BL Lac objects.