Quasar Lenses in the South: searches over the DES public footprint

TL;DR

This study conducted a comprehensive search for strongly lensed quasars over 5000 square degrees in the Southern Sky using five different source-oriented methods, successfully identifying known lenses and discovering new high-grade candidates for follow-up.

Contribution

It compares the effectiveness of multiple lens search methods and presents new high-confidence quasar lens candidates, including two previously unknown quadruplets.

Findings

Recovered 13 known lenses, including 8 quadruplets

The WISE and Gaia-DR2 based method was most effective

Identified two new high-grade lens candidates

Abstract

We have scanned 5000 deg$^{2}$ of Southern Sky to search for strongly lensed quasars with five methods, all source-oriented, but based on different assumptions and selection criteria. We analyse morphological searches based on Gaia multiplet detection and chromatic offsets, fibre-spectroscopic preselection, and X-ray and radio preselection. The performance and complementarity of the methods are evaluated on a common sample of known lenses in the Dark Energy Survey public DR1 footprint. We recovered in total 13 known lenses, of which 8 quadruplets. The method that found the largest number of known lenses is the one based on morphological and colour selection of objects from the WISE and Gaia-DR2 Surveys. We finally present a list of high-grade candidates from each method, to facilitate follow-up spectroscopic campaigns, including two previously unknown quadruplets: WG210014.9-445206.4 and WG021416.37-210535.3.