Deep radio maps of high-frequency selected BL Lac objects

The authors have made deep radio maps of five "ultracompact" BL Lac objects discovered because of their strong high-frequency radio emission. In three cases they detect substantial diffuse emission associated with the strong compact cores. The radio core emission is thought to be beamed towards the observer, while the diffuse emission is almost certainly isotropic. Therefore, the diffuse emission provides information on the properties of analogous but misdirected objects. At least in the cases in which diffuse emission is detected, the parent population of misdirected sources would have to be normal double radio sources.