Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-05-06
Astronomy and Astrophysics
Astrophysics
29 pages, 47 figures, accepted AJ
Scientific paper
10.1086/321179
We present new optical and near-IR spectroscopy as well as new high dynamic range, arcsecond-resolution VLA radio maps of BL Lacs from the complete radio-selected "1 Jansky" (1Jy) sample (RBLs) for which such data were not previously available. Unlike BL Lacs from the complete X-ray-selected Einstein Medium Sensitivity Survey (EMSS) sample (XBLs), most RBLs possess weak but moderately luminous emission lines. And whereas nearly all XBLs have extended power levels consistent with FR-1s, more than half of the RBLs have extended radio power levels too luminous to be beamed FR-1 radio galaxies. In fact, we find evidence for and examples of three distinct mechanisms for creating the BL Lac phenomenon in the 1Jy sample: beamed FR-1s, beamed FR-2s and possibly a few gravitationally-lensed quasars. The v/v_max determined for the 1Jy sample is 0.614+/-0.047, which is markedly different from the negative evolution seen in the EMSS and other XBL samples. A correlation between logarithmic X-ray to radio flux ratio and v/v_max is observed across the EMSS and 1Jy samples, from negative evolution in the more extreme XBLs to positive evolution in the more extreme RBLs. There is evidence that the selection criteria chosen by Stickel et al. eliminates some BL Lac objects from the 1Jy sample, although how many is unknown. And several objects currently in the sample have exhibited strong emission lines in one or more epochs, suggesting they should be reclassified as FSRQs. However these selection effects cannot account for the observed discrepancy in XBL and RBL properties. From these observational properties we conclude that RBLs and XBLs cannot be related by viewing angle alone, and that RBLs are more closely related to FSRQs.
Rector Travis A.
Stocke John T.
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