The quasar-galaxy cross SDSS J1320+1644: A probable large-separation lensed quasar

TL;DR

This paper reports the discovery of a probable large-separation lensed quasar system with two quasars and a galaxy group acting as a gravitational lens, supported by imaging, spectral analysis, and lens modeling.

Contribution

It presents the identification of a new gravitational lens candidate involving a quasar pair and a galaxy group, with detailed analysis of the lensing mass and environment.

Findings

Quasar pair at redshift 1.487 separated by 8.585 arcseconds.

Presence of two galaxies at redshift 0.899 forming a lensing system.

Estimated dark matter halo mass of approximately 4 x 10^{14} solar masses.

Abstract

We report the discovery of a pair of quasars at $z=1.487$, with a separation of $8\farcs585\pm0\farcs002$. Subaru Telescope infrared imaging reveals the presence of an elliptical and a disk-like galaxy located almost symmetrically between the quasars, creating 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 these galaxies are not isolated, but must be embedded in a dark matter halo of virial mass $\sim 4 \times 10^{14}\ h_{70}^{-1}\ {M}_\odot$ assuming an NFW model with a concentration parameter of $c_{vir}=6$, or a singular isothermal sphere profile with a velocity dispersion of $\sim 670$ 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.