The STRong lensing Insights into the Dark Energy Survey (STRIDES) 2017/2018 follow-up campaign: discovery of 10 lensed quasars and 10 quasar pairs

C LemonM W AugerR McMahonT AnguitaY ApostolovskiG C-F ChenC D FassnachtA D MeloMotta, VeronicaVeronicaMottaA ShajibT TreuA AgnelloE Buckley-GeerP L SchechterS BirrerT CollettF CourbinC E RusuT M C AbbottS AllamJ AnnisS AvilaE BertinD BrooksD L BurkeA Carnero RosellM Carrasco KindJ CarreteroM CostanziL N da CostaJ De VicenteS DesaiT F EiflerB FlaugherJ FriemanJ García-BellidoE GaztanagaD W GerdesD GruenR A GruendlJ GschwendG GutierrezK HonscheidD J JamesA KimE KrauseK KuehnN KuropatkinO LahavM LimaH LinM A G MaiaM MarchJ L MarshallF MenanteauR MiquelA PalmeseF Paz-ChinchónA A PlazasA RoodmanE SanchezM SchubnellS SerranoM SmithM Soares-SantosE SuchytaG TarleA R Walker2025-04-142025-04-142020-03-0910.1093/mnras/staa652https://cris-uv.scimago.es/handle/123456789/2362WOS:000535882100036ABSTRACT We report the results of the STRong lensing Insights into the Dark Energy Survey (STRIDES) follow-up campaign of the late 2017/early 2018 season. We obtained spectra of 65 lensed quasar candidates with ESO Faint Object Spectrograph and Camera 2 on the NTT and Echellette Spectrograph and Imager on Keck, confirming 10 new lensed quasars and 10 quasar pairs. Eight lensed quasars are doubly imaged with source redshifts between 0.99 and 2.90, one is triply imaged (DESJ0345−2545, z = 1.68), and one is quadruply imaged (quad: DESJ0053−2012, z = 3.8). Singular isothermal ellipsoid models for the doubles, based on high-resolution imaging from SAMI on Southern Astrophysical Research Telescope or Near InfraRed Camera 2 on Keck, give total magnifications between 3.2 and 5.6, and Einstein radii between 0.49 and 1.97 arcsec. After spectroscopic follow-up, we extract multi-epoch grizY photometry of confirmed lensed quasars and contaminant quasar + star pairs from DES data using parametric multiband modelling, and compare variability in each system’s components. By measuring the reduced χ2 associated with fitting all epochs to the same magnitude, we find a simple cut on the less variable component that retains all confirmed lensed quasars, while removing 94 per cent of contaminant systems. Based on our spectroscopic follow-up, this variability information improves selection of lensed quasars and quasar pairs from 34-45 per cent to 51–70 per cent, with most remaining contaminants being star-forming galaxies. Using mock lensed quasar light curves we demonstrate that selection based only on variability will over-represent the quad fraction by 10 per cent over a complete DES magnitude-limited sample, explained by the magnification bias and hence lower luminosity/more variable sources in quads.acceso abiertoASTRONOMY ASTROPHYSICSThe STRong lensing Insights into the Dark Energy Survey (STRIDES) 2017/2018 follow-up campaign: discovery of 10 lensed quasars and 10 quasar pairsjournal-article