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Reference: Marshall, PJ, Verma, A, More, A et al., (2015). Space Warps: I. Crowd-sourcing the discovery of gravitational lenses. Monthly Notices of the Royal Astronomical Society, 455 (2), 1171-1190.Citable link to this page:


Space Warps: I. Crowd-sourcing the discovery of gravitational lenses

Abstract: We describe SpaceWarps, a novel gravitational lens discovery service that yieldssamples of high purity and completeness through crowd-sourced visual inspection.Carefully produced colour composite images are displayed to volunteers via a webbasedclassification interface, which records their estimates of the positions of candidatelensed features. Images of simulated lenses, as well as real images which lacklenses, are inserted into the image stream at random intervals; this training set is usedto give the volunteers instantaneous feedback on their performance, as well as to calibratea model of the system that provides dynamical updates to the probability that aclassified image contains a lens. Low probability systems are retired from the site periodically,concentrating the sample towards a set of lens candidates. Having divided 160square degrees of Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) imaginginto some 430,000 overlapping 82 by 82 arcsecond tiles and displaying them on thesite, we were joined by around 37,000 volunteers who contributed 11 million imageclassifications over the course of 8 months. This Stage 1 search reduced the sampleto 3381 images containing candidates; these were then refined in Stage 2 to yield asample that we expect to be over 90% complete and 30% pure, based on our analysisof the volunteers performance on training images. We comment on the scalability ofthe SpaceWarps system to the wide field survey era, based on our projection thatsearches of 105 images could be performed by a crowd of 105 volunteers in 6 days.

Peer Review status:Peer reviewedPublication status:PublishedVersion:Accepted ManuscriptNotes:Copyright © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Marshall, P. J., Verma, A., More, A., Davis, C. P., More, S., Kapadia, A., … Collett, T. E. (2015, November 11). SPACE WARPS - I. Crowdsourcing the discovery of gravitational lenses. Monthly Notices of the Royal Astronomical Society. Oxford University Press (OUP). is available online at:

Bibliographic Details

Publisher: Oxford University Press

Publisher Website:

Journal: Monthly Notices of the Royal Astronomical Societysee more from them

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Issue Date: 2015


Urn: uuid:cbcd307f-70db-4af4-b4b6-e4ca752bea97

Source identifier: 518856

Eissn: 1365-2966


Issn: 0035-8711 Item Description

Type: Journal article;

Version: Accepted ManuscriptKeywords: gravitational lensing: strong methods: statistical methods: citizen science Tiny URL: pubs:518856


Autor: Marshall, PJ - institutionUniversity of Oxford Oxford, MPLS, Physics, Astrophysics fundingInstitute of Astronomy and Astrophysics



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