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

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 COOL J1153+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 (COOL J1153A) and a dust-obscured Type II quasar at z = 1.939 (COOL J1153B), 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 kpc) ∼ 3.3 × 1014M⊙ and relative time delays between the three brightest images of each quasar of Δt A3, A1 ∼ 800, Δt A2, A1 ∼ 1200, Δt B1, B3 ∼ 800, and Δt B2, B3 ∼ 1000 days. COOL J1153A resides in a dense environment with three nearby galaxies, two of which are also strongly lensed. We identified COOL J1153+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. COOL J1153+0755 expands the WSLQ sample from seven to eight systems (nine individual quasars), adding two powerful laboratories for probing black hole-galaxy coevolution at Cosmic Noon and for time-delay cosmography constraints on the Hubble constant, H0.