The Gravitational Lens Candidate FBQ 1633+3134

Abstract

We present our ground-based optical imaging, spectral analysis, and high-resolution radio mapping of the gravitational lens candidate FBQ 1633+3134. This z = 1.52, B = 17.7 quasar appears double on CCD images with an image separation of 066 and a relatively constant flux ratio of ∼3 : 1 across B, V, R, and I filters. A single 0.27 mJy radio source is detected at 8.46 GHz, coincident within an arcsecond of both optical components, but no companion at radio wavelengths is detected for the system down to a flux level of 0.1 mJy (3 σ). Spectral observations reveal a rich metal-line absorption system consisting of a strong Mg II doublet and associated Fe I and Fe II absorption features, all at an intervening redshift of z = 0.684, suggestive of a lensing galaxy. Point-spread function subtraction of ground-based images however shows no obvious signs of a third object between the two quasar images and places a detection limit of I ≳ 23.0 if such an object exists. Although the possibility that FBQ 1633+3134 is a binary quasar cannot be ruled out, the evidence presented here is consistent with FBQ 1633+3134 being a single quasar lensed by a faint, metal-rich galaxy.