Hunting high-redshift BL Lacs using Swift and SARA

BL Lacertae (BL Lac) objects are a sub-population of the blazar class of AGN where the relativistic jet is oriented along our line of sight. They are prominent members of Fermi Large Area Telescope catalogs and exhibit featureless optical spectra, which renders the redshift measurement a challenging effort. Indeed, half of the members of the BL Lac population lack redshift measurements. We employ the photometric dropout technique to establish redshifts for such sources. We use Swift-UVOT and two optical telescopes, the 0.65 m SARA-CT in Chile and 1.0 m SARA-ORM in the Canary Islands, Spain to obtain the desired redshift values. Using this method, we have been able to expand the class of high-z BL Lacs, which now counts up ~30 objects. In this contribution we will discuss the importance of these sources in probing the extragalactic background light and their potential to emit high energy neutrinos.