RADIO-LOUD ACTIVE GALAXIES IN THE NORTHERN ROSAT ALL-SKY SURVEY - III- NEW SPECTROSCOPIC IDENTIFICATIONS FROM THE RASS-GREEN BANK BL LACERTAE SURVEY

We present new spectroscopic identifications for 169 objects in the RA SS-Green Bank (RGB) catalog of radio- and X-ray-emitting active galact ic nuclei (AGNs). The data presented here significantly increase the f raction of bright RGB objects with classifications. Specifically, we r eport and discuss the classification of 57 radio-loud quasars, eight r adio-quiet quasars (QSOs), 53 BL Lacs, 32 broad-line radio galaxies, f ive narrow-line radio galaxies, three Seyfert I galaxies, and II galax ies or galaxies in clusters. Over 78% of the identifications we presen t here are the first published classifications for these sources. The observations we report were undertaken as part of our targeted search program to identify a new, large unbiased sample of BL Lac objects, an d we therefore discuss the BL Lac sample extensively. Unlike many prev ious surveys, we impose no selection criteria based on optical morphol ogy, color, or broadband spectral energy distribution. Our classificat ions are based solely on a carefully defined set of self-consistent sp ectroscopic classification criteria. These criteria are then carefully evaluated, and particular attention is paid to issues involving the c lassification and description of BL Lacs. The criteria yielded BL Lac classifications for 53 RGB objects, 38 of which were are newly discove red BL Lacs. We show these RGB BL Lacs exhibit transitional properties between normal galaxies and BL Lacs discovered in previous radio and X-ray surveys. We briefly discuss the broadband flux distributions of these new RGB BL Lacs and the range of Ca II H and K break contrasts ( Br-4000) they exhibit. We show that there is no clear separation in Br -4000 between BL Lacs and galaxies detected in the RGB survey, with th e distribution of break strengths varying smoothly between 0% and 50%. We also present and use a simple method based on the break strength t o estimate the contribution of both the host galaxy and AGN to the 400 0 Angstrom flux. We also show that the newly discovered RGB BL Lacs re side in a ''zone of avoidance'' in the log (S-x/S-r) versus log (S-o/S -r) diagram. This has important implications for BL Lac search strateg ies since it shows that RASS BL Lac samples will be severely incomplet e if candidates are chosen only from among those objects with the high est S-x/S-r flux ratios.