Cited by 116Galaxies: Formation, Evolution, PhenomenaAstrophysical Phenomena and ObservationsCosmology and Gravitation Theories

Space Warps– II. New gravitational lens candidates from the CFHTLS discovered through citizen science

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More, Anupreeta, Verma, Aprajita, Marshall, Philip J., More, Surhud, Baeten, Elisabeth, Wilcox, Julianne, Macmillan, Christine, Cornen, Claude +13 more·2016·Monthly Notices of the Royal Astronomical Society

Abstract

We report the discovery of 29 promising (and 59 total) new lens candidates from the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) based on about 11 million classifications performed by citizen scientists as part of the first Space Warps lens search. The goal of the blind lens search was to identify lens candidates missed by robots (the ringfinder on galaxy scales and arcfinder on group/cluster scales) which had been previously used to mine the CFHTLS for lenses. We compare some properties of the samples detected by these algorithms to the Space Warps sample and find them to be broadly similar. The image separation distribution calculated from the Space Warps sample shows that previous constraints on the average density profile of lens galaxies are robust. Space Warps recovers about 65 per cent of known lenses, while the new candidates show a richer variety compared to those found by the two robots. This detection rate could be increased to 80 per cent by only using classifications performed by expert volunteers (albeit at the cost of a lower purity), indicating that the training and performance calibration of the citizen scientists is very important for the success of Space Warps. In this work we present the SIMCT pipeline, used for generating in situ a sample of realistic simulated lensed images. This training sample, along with the false positives identified during the search, has a legacy value for testing future lens-finding algorithms. We make the pipeline and the training set publicly available.

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  • Even the largest citizen science lens search projects have only inspected up to around one million images.

    “Even the largest citizen science lens search projects have only inspected up to around one million images (Marshall et al. 2015; More et al. 2016; Sonnenfeld et al. 2020; González et al. 2025).”

    From Euclid Quick Data Release (Q1): XXVIII. The Strong Lensing Discovery Engine C – Finding lenses with machine learning (2026) · cites this paper as More et al. 2016

    Section 2.3 reports about 430,000 image cut-outs for the SPACE WARPS search, supporting that this project inspected fewer than one million images. The paper does not establish an upper limit for the largest citizen-science lens searches generally; its roughly 11 million classifications are repeat assessments, not distinct images. Page numbers are unavailable in our copy. (LLM, conf=0.82)

    Experimental — accuracy not yet measured
  • Previous lens-finding citizen-science projects have been able to search through a larger number of images (e.g. 430 000 in the CFHT Legacy Survey SW project).

    “Previous lens-finding citizenscience projects have been able to search through a larger number of images (e.g. 430 000 in the CFHT Legacy Survey SW project; see More et al. 2016)”

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Research works printed but not linked: 2

  1. Marshall P. et al., 2015, preprint (arXiv:1504.06148)(PaperI) · arXiv
  2. Thanjavur K. G., 2009, PhD thesis, Univ. Victoria, Canada

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Authors
More, A., Verma, A., Marshall, P. J., More, S., Baeten, E., Wilcox, J., Macmillan, C., Cornen, C., Kapadia, A., Parrish, M., Snyder, C., Davis, C. P., Gavazzi, R., Lintott, C. J., Simpson, R., Miller, D., Smith, A. M., Paget, E., Saha, P., Küng, R., & Collett, T. E.
Affiliations
  • Kavli Institute for the Physics and Mathematics of the Universe (JP)
  • University of Oxford (GB)
  • Adler Planetarium (US)
  • Kavli Institute for Particle Astrophysics and Cosmology (US)
  • Centre National de la Recherche Scientifique (FR)
  • University of Zurich (CH)
  • University of Portsmouth (GB)
Corresponding author
  • More, Anupreeta
  • Verma, Aprajita
  • Marshall, Philip J.
Venue
Monthly Notices of the Royal Astronomical Society
Published
2015-11-10
Volume
455
Issue
2
Pages
1191-1210
ISSN
  • 0035-8711 (ISSN-L)
  • 1365-2966
OpenAlex
W1793679032
Cited by
116
References
60
Citations by year
2026: 6 · 2025: 12 · 2024: 17 · 2023: 5 · 2022: 13 · 2021: 10 · 2020: 11 · 2019: 11 · 2018: 9 · 2017: 14 · 2016: 7 · 2015: 1
FWCI
5.88
Type
journal article
Language
en
Open access
Locations
  • Monthly Notices of the Royal Astronomical Society (publishedVersion)
  • Zurich Open Repository and Archive (University of Zurich) (acceptedVersion, other-oa)
  • arXiv (Cornell University) (submittedVersion)
  • reroDoc Digital Library (submittedVersion)
  • OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) (submittedVersion)
  • HAL (submittedVersion, other-oa)
  • HighWire Press Open Archive (submittedVersion)
  • Zurich Open Repository and Archive (University of Zurich) (submittedVersion, other-oa)
  • arXiv (Cornell University)
  • Zurich Open Repository and Archive (University of Zurich)
Funders
  • National Science Foundation (DE-AC02-76SF00515, 1066293)
  • U.S. Department of Energy (76SF00515, DE–AC02–76SF00515, AC02‐76SF00515, DE-AC02-)
  • Aspen Center for Physics (1066293, PHYS-1066293)
  • Leverhulme Trust
  • Ministry of Education, Culture, Sports, Science and Technology
  • Office of Science (AC02-76SF00515, DE-AC02-76SF0051 5, DE-AC02, 76SF00515)
  • Japan Society for the Promotion of Science (DE-AC02-76SF00515)
  • Basic Energy Sciences (DE-AC02, 76SF00515, AC02-76SF00515, DE-AC-02-76SF00515)
  • SLAC National Accelerator Laboratory (DEAC02−76SF00515, AC02‐76SF00515)
Topics
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Galaxies: Formation, Evolution, Phenomena
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
Keywords
gravitational lensing, citizen science, CFHTLS, false positives

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