Finding Multiply-Lensed and Binary Quasars in the DESI Legacy Imaging Surveys

TL;DR

This paper reports the discovery of 436 new multiply-lensed and binary quasar candidates in the DESI Legacy Imaging Surveys, significantly expanding the sample for cosmological measurements like the Hubble constant.

Contribution

The study introduces an autocorrelation-based search method applied to DESI data, resulting in a large new catalog of lensed quasar candidates with spectroscopic follow-up.

Findings

Discovered 436 new quasar candidates, including 65 with SDSS redshifts.

Applied an autocorrelation algorithm to identify lens candidates.

Provided redshifts for additional candidates from spectroscopic data.

Abstract

The time delay between multiple images of strongly lensed quasars is a powerful tool for measuring the Hubble constant (H0). To achieve H0 measurements with higher precision and accuracy using the time delay, it is crucial to expand the sample of lensed quasars. We conduct a search for strongly lensed quasars in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys. The DESI Legacy Surveys comprise 19,000 deg2 of the extragalactic sky observed in three optical bands (g, r, and z), making it well suited for the discovery of new strongly lensed quasars. We apply an autocorrelation algorithm to ~5 million objects classified as quasars in the DESI Quasar Sample. These systems are visually inspected and ranked. Here, we present 436 new multiply lensed and binary quasar candidates, 65 of which have redshifts from Sloan Digital Sky Survey Data Release 16. We provide redshifts for an additional 18 candidates from the SuperNova Integral Field Spectrograph.