Session 10 - AGN - Host Galaxies & Environment.
Display session, Monday, January 13
Metropolitan Ballroom,

[10.01] The Large-scale Environments of Radio Galaxies and BL Lacertae Objects

J. E. Pesce, M. O'Dowd, R. Scarpa, C. M. Urry (STScI), R. Falomo (Padua Obs.), J. Kim (Towson State Univ.), A. Paske (Pomona College)

The study of BL Lac environments is hindered by the lack of knowledge regarding the environments of their putative parents, the FRI/II radio galaxies. To rectify this we have assembled a complete sample of FRI/II radio galaxies with z \leq 0.15 from the 2 Jy (Wall amp; Peacock 1985) and Ekers et al. (1989) lists, about 100 objects in total. The analysis of the galaxy properties is presented elsewhere. Here we give results of the study of their environments performed using digitized sky survey plates (POSS and ESO-SERC). The radio galaxy environments are compared to those of a matched (z \leq 0.15), complete sample of BL Lac objects from the same plate material.

In addition, a Hubble Space Telescope Snapshot project to obtain WFPC2 images of 132 BL Lac objects is currently underway. The targets include all BL Lacs in large complete samples (e.g., EMSS, 1 Jy, HEAO, etc.) and range in redshift from approximately 0.03 to 1.1. To date, we have about one-half of the sample and are presently studying the BL Lac host galaxy properties. Here we present the analysis of the extended (out to 60 - 600 kpc, for z = 0.03 - 1.1) environments around the target BL Lac objects. The HST data are used to determine excess galaxy counts above the background, to determine the morphological classification of the surrounding galaxies themselves, and to look for nearby companions and signs of interaction. The study will allow us to search for evolutionary effects in environmental properties and differences between X-ray selected and radio-selected BL Lacs and will complement the study of the fields of low redshift radio galaxies.