Quasars Acting as Strong Lenses Found in DESI DR1

McArthur, E.; Millon, M.; Powell, M.; Wechsler, R. H.; Pan, Z.; Siudek, M.; Spiller, J.; Aguilar, J.; Ahlen, S.; Anand, A.; BenZvi, S.; Bianchi, D.; Brooks, D.; Claybaugh, T.; Cuceu, A.; de la Macorra, A.; Dey, Arjun; Doel, P.; Font-Ribera, A.; Forero-Romero, J. E.; Gaztañaga, E.; Gontcho A Gontcho, S.; Gutierrez, G.; Herrera-Alcantar, H. K.; Honscheid, K.; Ishak, M.; Joyce, R.; Juneau, S.; Kirkby, D.; Kisner, T.; Kremin, A.; Lahav, O.; Lamman, C.; Landriau, M.; Le Guillou, L.; Manera, M.; Meisner, A.; Miquel, R.; Nadathur, S.; Palanque-Delabrouille, N.; Percival, W. J.; Poppett, C.; Prada, F.; Pérez-Ràfols, I.; Rossi, G.; Sanchez, E.; Schlegel, D.; Schubnell, M.; Seo, H.; Silber, J.; Sprayberry, D.; Tarlé, G.; Weaver, B. A.; Zhou, R.; Zou, H.; DESI Collaboration
Bibliographical reference

The Astrophysical Journal

Advertised on:
8
2026
Number of authors
56
IAC number of authors
1
Citations
1
Refereed citations
0
Description
Quasars acting as strong gravitational lenses offer a rare opportunity to probe the redshift evolution of scaling relations between supermassive black holes and their host galaxies, particularly the MBH─Mhost relation. Using these powerful probes, the mass of the host galaxy can be precisely inferred from the Einstein radius θE. Using 812,118 quasars from DESI DR1 (0.03 ≤ z ≤ 1.8), we searched for quasars lensing higher-redshift galaxies by identifying background emission-line features in their spectra. To detect these rare systems, we trained a convolutional neural network (CNN) on mock lenses constructed from real DESI spectra of quasars and emission-line galaxies (ELGs), achieving a high classification performance (AUC = 0.99). We also trained a regression network to estimate the redshift of the background ELG. Applying this pipeline, we identified seven high-quality (Grade A) lens candidates, each exhibiting a strong [O II] doublet at a higher redshift than the foreground quasar; four candidates additionally show Hβ, [O III] λ4959, and [O III] λ5007 emission. These results significantly expand the sample of quasar lens candidates beyond the 12 identified and 3 confirmed in previous work and demonstrate the potential for scalable, data-driven discovery of quasars as strong lenses in upcoming spectroscopic surveys.