Discovery of 19 strongly lensed, dual, or projected quasars in DESI-LS

¹ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, Jiangsu 210023, China
² School of Physics and Astronomy, Beijing Normal University, Beijing 100875, China
³ Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
⁴ School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei 230026, China
⁵ Institute for Astrophysics, School of Physics, Zhengzhou University, Zhengzhou 450001, China
⁶ Key Lab of Space Astronomy and Technology, National Astronomical Observatories, 20A Datun Road, Chaoyang District, Beijing 100012, China
⁷ Centre for Fundamental Physics, School of Mechanics and Optoelectric Physics, Anhui University of Science and Technology, Huainan, Anhui 232001, China

^⋆ Corresponding author; zzhe@pmo.ac.cn

Received: 24 October 2024
Accepted: 14 January 2025

Abstract

We report the results of a follow-up spectroscopic confirmation of two lensed quasars, six dual quasars, and eleven projected quasars that had previously been identified as lensed-quasar candidates in our earlier work. The spectroscopic data were obtained from two different sources: Palomar 200-inch Double Spectrograph (P200/DBSP) in California and publicly available datasets, including SDSS and DESI-EDR. The two lensed quasars (both pairs) have the following properties: θ_E = 1.″208, z_s = 3.105; θ_E = 0.″749, and z_s = 2.395. The six dual quasars have redshifts ranging from 0.58 to 3.28 and projected separations ranging from 15.44 to 22.54 kpc, with a mean separation of 17.95 kpc. The eleven projected quasars have projected separations ranging from 10.96 to 39.07 kpc, with a mean separation of 22.64 kpc. Additionally, there are three likely lensed quasars that cannot be definitively confirmed, included for two reasons. Firstly, their image separations (0.″83, 0.″98, and 0.″93) are small compared to the seeing conditions during our observations (around 1.″2). Secondly, no high signal-to-noise (S/N) lensing galaxy can be feasibly detected in Legacy Survey Imaging. Improved spectroscopy and/or imaging would be needed to confirm their lensing nature.