The Optical/Near-Infrared Colors of Broad Absorption Line Quasars, Including the Candidate Radio-loud Broad Absorption Line Quasar 1556+3517

A candidate radio-loud broad absorption line (RLBALQ) has been recently reported by Becker et al. We present JHK observations of this object and three other radio-detected BALQs taken with the new Michigan-Dartmouth-MIT/Ohio State/Aladdin Infrared Camera (MOSAIC) on the KPNO 4 m telescope. The candidate RLBALQ 1556+3517 has B - K = 6.63, redder than all but one or two known z > 1 quasars. This strongly suggests that the observed continuum of this quasar is reddened by dust. Even when this extreme reddening is taken into account, 1556+3517 is still probably radio loud, although near-infrared spectroscopy to measure its Balmer decrement will be needed to verify this. In addition, since it is a flat-spectrum object, VLBI observations to determine the extent (if any) to which beaming affects our estimate of its radio luminosity will be needed before 1556+3517 can be unequivocally declared a radio-loud BALQ. We also use our data and data from the literature to show that optically selected BALQs as a class have B - K colors consistent with the observed distribution for optically selected quasars as a whole. Thus, there is currently no evidence that the tendency of optically selected BALQs to be preferentially radio intermediate (see the work of Francis, Hooper, and Impey) is due to extinction artificially lowering estimated BALQ optical luminosities. However, as most quasar surveys, both radio and optical, would be insensitive to a population of reddened radio-quiet BALQs, the existence of a large population of reddened BALQs similar to 1556+3517 cannot yet be ruled out.