Clustering environments of BL Lac objects

Abstract

We report measurements of the amplitude of the BL Lac galaxy spatial covariance function, B_gb_, for the fields of five BL Lacertae objects. We present evidence for rich clusters around MS 1207+39 and MS 1407+59, and confirm high richness for the cluster containing H0414+009. We discuss the case of 3C 66A and find evidence for a poor cluster based on an uncertain redshift of z=0.444. These data suggest that at least some BL Lac objects are consistent with being FR 1 radio galaxies in rich clusters.