A Search for Gravitationally Lensed Quasars and Quasar Pairs in Pan-STARRS1: Spectroscopy and Sources of Shear in the Diamond 2M1134$-$2103

TL;DR

This paper reports a systematic search for gravitationally lensed quasars in Pan-STARRS1, discovering 91 candidates, including a new quadruply lensed quasar with detailed mass modeling revealing the influence of nearby structures.

Contribution

It introduces a new candidate list of lensed quasars from Pan-STARRS1 and provides the first spectroscopic confirmation and detailed mass modeling of a specific quadruply lensed quasar, 2M1134-2103.

Findings

91 quasar lens candidates identified

Spectroscopic confirmation of 2M1134-2103 with redshift 2.77

Large shear explained by nearby faint companion and galaxy group/cluster

Abstract

We present results of a systematic search for gravitationally lensed quasars in Pan-STARRS1. Our final sample of candidates comprises of 91 systems, not including 25 rediscovered lensed quasars and quasar pairs. In the absence of spectroscopy to verify the lensing nature of the candidates, the main sources of contaminants are likely to be quasar pairs, which we consider to be a byproduct of our work, and a smaller number of quasar$+$star associations. Amongst the independently discovered quads is 2M1134$-$2103, for which we obtained spectroscopy for the first time, finding a redshift of 2.77 for the quasar. There is evidence for microlensing in at least one image. We perform detailed mass modeling of this system using archival imaging data, and find that the unusually large shear responsible for the diamond-like configuration can be attributed mainly to a faint companion $\sim 4''$ away, and to a galaxy group/cluster $\sim 30''$ away. We also set limits of $z\sim0.5-1.5$ on the redshift of the lensing galaxy, based on its brightness, the image separation of the lensed images, and an analysis of the observed photometric flux ratios.