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Inconsistent (or Inconsistently Applied) Identification Criteria

As we mentioned in § 3, there has not, to date, been either a single definition of the blazar class or of the BL Lac and FSRQ subclasses. The literature contains several examples of such inconsistencies. For example, as pointed out by Perlman et al. (1996b), the lack of a Ca II H & K break strength criterion in the 1 Jy, S4 and S5 samples of BL Lacs, has caused numerous objects to be misclassified as radio galaxies instead of BL Lacs (see also Marchã & Browne 1995, 1996). It is therefore likely that a number of low-z objects may have been missed in this fashion.

Similarly, inspection of the spectra of 1 Jy BL Lacs (Stickel et al. 1993) reveals several which have emission lines considerably stronger than $W_\lambda = 5(1+z)$ Å. While one may argue that some of these objects fall in the expanded region of the (H & K break strength, equivalent width) diagram that Marchã et al. (1996) allot to the BL Lacs, several, for example 1 Jy 1308+326, do not. The majority of these broad-line objects are at z>0.5 and they may be the reason why the redshift distribution of the 1 Jy BL Lac sample is so dissimilar from the EMSS, Slew and DXRBS BL Lac redshift distribution. The variable nature of blazars makes this a particularly thorny problem to deal with. It is well known that several BL Lacs exhibit emission lines in their faint states (as we mentioned in § 3). Therefore it is entirely possible that the classification of a given object may be related to the state it was in when its classification spectrum was taken.

A third facet of this problem is the question of whether all flat-spectrum, broad-lined objects deserve to be called FSRQs. We believe this to be the case, based upon the general similarities of properties between BLRGs and FSRQs (e.g., Siebert et al. 1996). However we should note that the intrinsic power of the AGN affects how a source will be classified (see above). Others, however, have taken a different approach, and as a result some of the previously-identified objects which we list as FSRQs in Table 6 have been classified as BLRGs by other authors.