paper

Confirming HSC strong lens candidates with DESI Spectroscopy. I. Project overview and first results

arXiv:2505.16158 · doi:10.1007/s11433-025-2747-4

Abstract

Accurate redshift determinations of both lenses and sources are critical for confirming strong-lens systems and fully realizing their scientific value. However, the thousands of strong-lens candidates now routinely discovered in wide-field imaging surveys make one-by-one follow-up observations impractical. In this work, we investigate the capability and efficiency of large-scale spectroscopic surveys in confirming strong-lens systems. As a case study, we cross-match strong lens candidates identified from the Hyper Suprime-Cam Subaru Strategic Program with Data Release 1 (DR1) of the Dark Energy Spectroscopic Instrument (DESI). We find that DESI DR1 serendipitously observed putative lenses and/or lensed images in approximately 50\% of these candidates. Analyzing the DESI spectra for matched candidates that meet our selection criteria, we determine both lens and source redshifts for 27 systems. Additionally, 76 candidate systems feature lensing galaxies at , and one candidate system contains a quasar within its lensing galaxy. Applying this approach to other strong-lens candidates will yield many more confirmations, with a further several-fold increase anticipated from the final DESI data release. Our results highlight the growing importance of large-scale spectroscopic surveys in advancing strong lensing discoveries and science.

28 pages, 4 figures, 3 tables, published in SCIENCE CHINA Physics, Mechanics & Astronomy. A new figure (Figure 1) was added to this version, showing the redshift vs. magnitude distributions of the lenses and lensed images

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