Astronomy and Astrophysics, volume 381, 810-824 (2002/1-3)
Deep optical imaging of radio selected BL Lacertae objects.
PURSIMO T., NILSSON K., TAKALO L.O., SILLANPAEAE A., HEIDT J. and PIETILAE H.
Abstract (from CDS):
Deep imaging data on radio-selected BL Lacertae objects are presented. The complete 1Jy sample consists of 37 objects. Altogether 25 objects were observed which span a large range of redshifts (up to z=1.34) with 12 objects having z>0.5. In addition, three objects are located at an unknown distance. Altogether in eleven objects the host galaxy could be resolved. All nine objects with z≲0.4 were resolved and all eleven objects with z>0.7 or unknown redshift were unresolved. In all (six) low-z (z≲0.2) objects, an elliptical host galaxy was preferred. Of the remaining objects, only in one case (2007+777) did a disc-type galaxy give better fit than elliptical, but in this case neither can be preferred. The absolute brightness of the host galaxies (median MR=-23.82) is similar to the findings of X-ray selected BL Lacs and low redshift radio galaxies. Also the sizes (median re=14.8kpc) of the galaxies are similar. This supports the idea that (at least low redshift) BL Lacs belong to one family of objects. These results agree well with other recent studies on BL Lacs. There is a strong correlation between the brightness of the active nucleus and redshift. At low redshift radio and X-ray selected BL Lacs have similar brightnesses. No (or only weak) correlation was found between the brightness of the nucleus and the host galaxy.