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

Research output: Contribution to journalArticlepeer-review

  • C. Lemon
  • M. W. Auger
  • R. McMahon
  • T. Anguita
  • Y. Apostolovski
  • G. C.-F. Chen
  • C. D. Fassnacht
  • A. Melo
  • V. Motta
  • A. Shajib
  • T. Treu
  • A. Agnello
  • E. Buckley-Geer
  • P. L. Schechter
  • S. Birrer
  • F. Courbin
  • C. E. Rusu
  • T. M. C. Abbott
  • S. Allam
  • J. Annis
  • S. Avila
  • E. Bertin
  • D. Brooks
  • D. L. Burke
  • A. Carnero Rosell
  • M. Carrasco Kind
  • J. Carretero
  • M. Costanzi
  • L. N. da Costa
  • J. De Vicente
  • S. Desai
  • T. F. Eifler
  • B. Flaugher
  • J. Frieman
  • J. García-Bellido
  • E. Gaztanaga
  • D. W. Gerdes
  • D. Gruen
  • R. A. Gruendl
  • J. Gschwend
  • G. Gutierrez
  • K. Honscheid
  • D. J. James
  • A. Kim
  • E. Krause
  • K. Kuehn
  • N. Kuropatkin
  • O. Lahav
  • M. Lima
  • H. Lin
  • M. A. G. Maia
  • M. March
  • J. L. Marshall
  • F. Menanteau
  • R. Miquel
  • A. Palmese
  • F. Paz Chinchón
  • A. A. Plazas
  • A. Roodman
  • E. Sanchez
  • M. Schubnell
  • S. Serrano
  • M. Smith
  • M. Soares-Santos
  • E. Suchyta
  • G. Tarle
  • A. R. Walker
We report the results of the STRong lensing Insights from the Dark Energy Survey (STRIDES) follow-up campaign of the late 2017/early 2018 season. We obtained spectra of 65 lensed quasar candidates with EFOSC2 on the NTT and ESI 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 SOAR or NIRC2 on Keck, give total magnifications between 3.2 and 5.6, and Einstein radii between 0.49 and 1.97 arcseconds. After spectroscopic follow-up, we extract multi-epoch grizY photometry of confirmed lensed quasars and contaminant quasar+star pairs from DES data using parametric multi-band 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 lightcurves 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.
Original languageEnglish
Pages (from-to)3491-3511
Number of pages21
JournalMonthly Notices of the Royal Astronomical Society
Volume494
Issue number3
Early online date9 Mar 2020
DOIs
Publication statusPublished - 1 May 2020

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    Rights statement: This article has been accepted for publication in MNRAS © 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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