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1504.06148
Space Warps: I. Crowd-sourcing the discovery of gravitational lenses
Marshall, et al
Space Warps is a novel GL discovery service that yields samples of high purity and completeness through crowd-sourced visual inspection. Carefully produced color composite images are displayed to volunteers via a classification interface which records their estimates of the positions of candidate lensed features. Simulated lenses, and expert-classified images which lack lenses, are inserted into the image stream at random intervals; this training set is used to give the volunteers feedback on their performance, as well as to calibrate it in order to allow dynamical updates to the probability of any image they classify to contain a lens Low probability systems are retired from the site periodically, concentrating the sample towards a set of candidates. Having divided 160 sq deg of CFHTLS imaging into some 430k overlapping 84x84" tiles and displaying them on the site, 37k volunteers joined who contributed 11e6 image classifications over the course of 8 months. The sample was reduced to 3368 Stage I candidates; these were then refined to yield a sample that are expected to be over 90% complete and 30% pure. Comment on the scalability of the Space Warps system to the wide field survey era, based on the finding that searches of 1e5 images can be performed by a crowd of 1e5 volunteers in 6 days.
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