Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aas...19310713r&link_type=abstract
American Astronomical Society, 193rd AAS Meeting, #107.13; Bulletin of the American Astronomical Society, Vol. 30, p.1412
Astronomy and Astrophysics
Astronomy
Scientific paper
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 < V/Vmax >\ value for the M91 sample to 0.399+/-0.057; and < V/Vmax >\ = 0.416+/-0.046 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.
Gioia Isabella Maria
Morris Simon L.
Perlman Eric Steven
Rector Travis A.
Stocke John T.
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