The impact of human expert visual inspection on the discovery of strong gravitational lenses

Karina Rojas, Thomas E. Collett, Daniel Ballard, Mark R. Magee, Simon Birrer, Elizabeth Buckley-Geer, James H. H. Chan, Benjamin Clément, José M. Diego, Fabrizio Gentile, Jimena González, Rémy Joseph, Jorge Mastache, Stefan Schuldt, Crescenzo Tortora, Tomás Verdugo, Aprajita Verma, Tansu Daylan, Martin Millon, Neal JacksonSimon Dye, Alejandra Melo, Guillaume Mahler, Ricardo L. C. Ogando, Frédéric Courbin, Alexander Fritz, Aniruddh Herle, Javier A. Acevedo Barroso, Raoul Cañameras, Claude Cornen, Birendra Dhanasingham, Karl Glazebrook, Michael N. Martinez, Dan Ryczanowski, Elodie Savary, Filipe Góis-Silva, L. Arturo Ureña-López, Matthew P. Wiesner, Joshua Wilde, Gabriel Valim Calçada, Rémi Cabanac, Yue Pan, Isaac Sierra, Giulia Despali, Micaele V. Cavalcante-Gomes, Christine Macmillan, Jacob Maresca, Aleksandra Grudskaia, Jackson H. O'Donnell, Eric Paic, Anna Niemiec, Lucia F. de la Bella, Jane Bromley, Devon M. Williams, Anupreeta More, Benjamin C. Levine

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We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with $g$-band signal-to-noise less than $\sim$25 or Einstein radii less than $\sim$1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifier's experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies.
Original languageEnglish
Pages (from-to)4413–4430
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Early online date7 Jun 2023
Publication statusPublished - 1 Aug 2023


  • gravitational lensing: strong
  • UKRI
  • STFC
  • ST/P006760/1

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