COOL-LAMPS IX: A Rare Duo of Quasars Each Lensed by a Single Massive Galaxy Cluster

TL;DR

This paper reports the discovery of a rare wide-separation lensed quasar system by the COOL-LAMPS collaboration, featuring two quasars each lensed by the same galaxy cluster, providing new opportunities for cosmology and galaxy evolution studies.

Contribution

The discovery of COOLJ1153+0755, expanding the sample of wide-separation lensed quasars from 7 to 8 systems, with detailed lens modeling and environmental analysis.

Findings

Two quasars each lensed into four images by the same cluster.

Estimated cluster mass of approximately 3.3×10^14 solar masses.

Identification of the system without morphological selection, indicating potential for discovering more such systems.

Abstract

Wide-separation lensed quasars (WSLQs) are rare systems that arise from the chance alignment of two objects: a galaxy cluster and a background quasar. After two decades, only seven WSLQs have been found. Here, we report the discovery of COOLJ1153+0755 by the COOL-LAMPS collaboration in DECaLS imaging and its confirmation with follow-up observations with the Magellan Telescopes and the Nordic Optical Telescope. This system features two multiply-imaged quasars each lensed into four images by the same $z=0.4301$ cluster: a classic broad-line Type I quasar at $z=1.524$ (COOLJ1153A) and a dust-obscured Type II quasar at $z=1.939$ (COOLJ1153B), with maximum image separations of $25.''6$ and $26.''0$, respectively. We construct a lens model to estimate a projected cluster mass of $M(<500\,{\rm kpc})\sim3.3\times10^{14}{\rm M}_{\odot}$ and relative time delays between the three brightest images of each quasar of $\Delta t_{\rm \,A3,A1}\sim800$, $\Delta t_{\rm \,A2,A1}\sim1200$, $\Delta t_{\rm \,B1,B3}\sim800$, and $\Delta t_{\rm \,B2,B3}\sim1000$ days. COOLJ1153A resides in a dense environment with three nearby galaxies, two of which are also strongly lensed. We identify COOLJ1153+0755 without making a morphological cut in the DECaLS catalog; none of its multiple images are classified as point sources in those data, implying that morphology-based selection would miss such systems. COOLJ1153+0755 expands the WSLQ sample from 7 to 8 systems (9 individual quasars), adding two powerful laboratories for probing black hole-galaxy co-evolution at Cosmic Noon and for time-delay cosmography constraints on the Hubble constant, $H_0$.