THE RECOGNITION OF BL LAC OBJECTS - EFFECTS ON REDSHIFT DISTRIBUTIONS, MISSING OBJECTS AND COSMOLOGICAL EVOLUTION

The fact that BLLac objects exist in the nuclei of host galaxies means that low-luminosity BLLacs are more difficult to recognize than more luminous ones. The failure to account for such a selection effect can lead to erroneous conclusions about the statistical properties of these objects. We quantify this effect and show how the method developed can be used to predict the redshift distribution and (V/V-max) for existing BLLac samples. The comparison between the predictions and observations suggests that objects have been missed in both the radio and X-ray samples of BLLacs. Although quantifying the selection effects can help us understand some of the characteristics of the observed distributions, they are not sufficient to account for the difference in the deduced rate of cosmological evolution between radio- and X-ray-selected objects. However, the combination of recognition effects and negative cosmological evolution enables us to obtain a good fit to the observed redshift distribution of the EMSS sample of BL Lac objects.