The DESI Single Fiber Lens Search. I. Four Thousand Spectroscopically Selected Galaxy-Galaxy Gravitational Lens Candidates

TL;DR

This paper reports the discovery of over four thousand strong gravitational lens candidates from DESI data, including many new ones, using spectral features indicative of lensing, and discusses their potential for cosmological studies.

Contribution

The study introduces a novel spectral method to identify a large sample of strong galaxy-galaxy lens candidates from DESI, significantly expanding the known lens catalog.

Findings

Identified 4,110 lens candidates, 3,887 of which are new.

Estimated 53% of candidates are true lenses with measurable Einstein radii.

Demonstrated potential for cosmological applications like H0 measurement and dark matter substructure analysis.

Abstract

We present 4,110 strong gravitational lens candidates, 3,887 of which are new discoveries, selected from a sample of 5,837,154 luminous red galaxies (LRGs) observed with the Dark Energy Spectroscopic Instrument (DESI). Candidates are identified via the presence of background ionized oxygen [O II] nebular emission lines in the foreground LRG spectra which may originate from the lensing of higher redshift star-forming galaxies. Using the measured foreground redshift, background redshift, and integrated flux of the background [O II] doublet, we integrate over impact parameters to compute the probability that each candidate is a lens. We expect 53% of candidates to be true lenses with Einstein radii ranging from 0.1'' to 4'', which can be confirmed with high-resolution imaging. Confirmed strong lenses from this sample will form a valuable cosmological dataset, as strong gravitational lensing is the only method to directly measure dark matter halo substructure at cosmological distances. We independently recover the host of the multiply imaged gravitationally lensed type Ia supernova iPTF16geu. Monitoring these lenses for future multiply lensed transients will enable (a) H0 measurements via time-delay cosmography and (b) substructure measurements via flux ratios.