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D. Londish (Jet Propulsion Laboratory, California Institute of Technology; University of Sydney), S.M. Croom (Anglo-Australian Observatory), J. Heidt (Landessternwarte Uni Heidelberg), B.J. Boyle. (Australia Telescope National Facility)
We present further studies of the 2dF BL Lac sample (the 2BL, Londish et al. 2002 MNRAS 334,941), the first optically selected sample of BL Lac objects identified from scrutiny of over 8000 spectra in two redshift surveys, the 2QZ and 6QZ (Croom et al.\,2001, MNRAS, 325, 483; MNRAS, 2004, 349, 1397). BL Lac objects are thought to be the beamed counterparts of FRI/FRII radio galaxies (cf. review by Urry & Padovani 1995, PASP, 107,803); at optical wavelengths these objects are dominated by Doppler boosted, synchrotron radiation, the resultant featureless continuum making them all but impossible to target in optical surveys. To date, therefore, all BL Lac samples have been initially identified in radio and/or X-ray surveys, with obvious bias against radio-quiet objects. In contrast the majority of 2BL objects (38/52) are radio-quiet.
Recent high signal-to-noise VLT spectra of 33 2BL objects has led us to re-classify 12 objects as weak-lined QSOs and a further 6 as white dwarfs/stars. Seven of the 15 remaining continuum objects are undetected at radio and X-ray frequencies. The puzzle remains as to why these radio-quiet QSOs are lineless, or why these beamed continuum objects are radio-quiet - is there a mechanism that produces radio-quiet jets?
The author(s) of this abstract have provided an email address for comments about the abstract: londish@ipac.caltech.edu
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.