The Quasar-galaxy Cross SDSS J1320+1644: A Probable Large-separation Lensed Quasar

We report the discovery of a pair of quasars at z = 1.487, with a separation of 8.''585 ± 0.''002. Subaru Telescope infrared imaging reveals the presence of an elliptical and a disk-like galaxy located almost symmetrically between the quasars, in a cross-like configuration. Based on absorption lines in the quasar spectra and the colors of the galaxies, we estimate that both galaxies are located at redshift z = 0.899. This, as well as the similarity of the quasar spectra, suggests that the system is a single quasar multiply imaged by a galaxy group or cluster acting as a gravitational lens, although the possibility of a binary quasar cannot be fully excluded. We show that the gravitational lensing hypothesis implies that these galaxies are not isolated, but must be embedded in a dark matter halo of virial mass ~4 × 10¹⁴ h ^-1 ₇₀ M _⊙ assuming a Navarro-Frenk-White model with a concentration parameter of c _vir = 6, or a singular isothermal sphere profile with a velocity dispersion of ~670 km s^-1. We place constraints on the location of the dark matter halo, as well as the velocity dispersions of the galaxies. In addition, we discuss the influence of differential reddening, microlensing, and intrinsic variability on the quasar spectra and broadband photometry.

Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Use of the UH2.2 m telescope for the observations is supported by NAOJ.