Session 84 - QSOs and BL Lacs.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center

[84.13] The Discovery of Low-Luminosity BL Lacs

T. A. Rector, J. T. Stocke (CASA - University of Colorado)

Many of the properties of BL Lacs have become explicable in terms of the relativistic beaming'' hypothesis whereby BL Lacs are highly beamed'' FR-I radio galaxies (i.e. our line of sight to these objects is nearly along the jet axis). Further, radio-selected BL Lacs (RBLs) are believed to be seen nearly on-axis'' (the line-of-sight angle \theta \sim 8\deg) while X-ray selected BL Lacs (XBLs) are seen at larger angles (\theta \sim 30\deg; the X-ray emitting jet is believed to be less collimated). However, a major problem with this model was that a transition population between beamed BL Lacs and unbeamed FR-Is had not been detected. Low-luminosity BL Lacs may be such a transition population, and were predicted to exist by Browne and Marcha (1993). We present ROSAT HRI images, VLA radio maps and optical spectra which confirm the existence of low-luminosity BL Lacs, objects which were previously mis-identified in the EMSS catalog as clusters of galaxies. Thus our results strengthen the relativistic beaming hypothesis.