Imaging Redshift Estimates for Fermi BL Lacs

Abstract

We have obtained WIYN and SOAR i' images of BL Lacertae objects (BL Lacs) and used these to detect or constrain the flux of the host galaxy. Under common standard candle assumptions these data provide estimates of, or lower bounds on, the redshift. Our targets are a set of flat-spectrum radio counterparts of high flux Fermi Large Area Telescope (LAT) sources, with sensitive spectral observations showing them to be continuum-dominated BL Lacs. In this sample 5 of 11 BL Lacs yielded significant host detections, with standard candle redshifts z=0.13-0.58. Our estimates and lower bounds are generally in agreement with other redshifts estimates, although our z=0.374 estimate for J0543-5532 implies a significantly sub-luminous host.