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T.A. Rector (NOAO), J.T. Stocke (CASA/Colorado), E.S. Perlman (STScI), S.L. Morris (DAO), I.M. Gioia (IfA/Hawaii)
We present updated, complete radio, optical and X-ray data for BL Lacs in the Einstein Medium Sensitivity Survey (EMSS). The complete ``M91" sample first presented in Morris et al. (1991) is updated; and we define a new, virtually complete sample consisting of 40 EMSS BL Lacs (the ``D40" sample). New high signal-to-noise, arcsecond-resolution VLA maps are also presented for ten EMSS BL Lacs, completing VLA observations of the M91 sample.
The addition of four new objects and updated X-ray flux and redshift information has increased the \langle V/Vmax \rangle\ value for the M91 sample to 0.399±.057; and \langle V/Vmax \rangle\ = 0.416±.046 for the newly defined D40 sample. In conjunction with the results of Bade et al. (1998) these results strongly establish negative evolution for X-ray-selected BL Lac Objects. The positive evolution seen in radio-selected BL Lacs poses a significant problem for the unified model. Also, our VLA observations of the M91 sample confirm that X-ray-selected BL Lacs are too core-dominated to be consistent with a beamed population of FR-1s seen at an intermediate angles for the moderate outflow velocities (\gamma ~5) suggested for XBL emitting regions. The observed spectral and radio properties of XBLs, however, are completely consistent with XBLs being the beamed population of low-luminosity, FR-1 radio galaxies.
The author(s) of this abstract have provided an email address for comments about the abstract: rector@noao.edu