Automated detection of galaxy-scale gravitational lenses in high resolution imaging data

• Published in: arXiv.org 2008-05
• Main Authors: Marshall, Philip J, Hogg, David W, Moustakas, Leonidas A, Fassnacht, Christopher D, Bradac, Marusa, Schrabback, Tim, Blandford, Roger D
• Format: Article
• Language: English
• Subjects: Astronomical models; Automation; Classification; Completeness; Computer simulation; Conditional probability; Galaxies; Gravitation; Gravitational lenses; Image resolution; Probabilistic inference; Probability distribution; Quality assessment; Rejection rate; Robots
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0805.1469

Lens modeling is the key to successful and meaningful automated strong galaxy-scale gravitational lens detection. We have implemented a lens-modeling "robot" that treats every bright red galaxy (BRG) in a large imaging survey as a potential gravitational lens system. Using a simple model optimized for "typical" galaxy-scale lenses, we generate four assessments of model quality that are used in an automated classification. The robot infers the lens classification parameter H that a human would have assigned; the inference is performed using a probability distribution generated from a human-classified training set, including realistic simulated lenses and known false positives drawn from the HST/EGS survey. We compute the expected purity, completeness and rejection rate, and find that these can be optimized for a particular application by changing the prior probability distribution for H, equivalent to defining the robot's "character." Adopting a realistic prior based on the known abundance of lenses, we find that a lens sample may be generated that is ~100% pure, but only ~20% complete. This shortfall is due primarily to the over-simplicity of the lens model. With a more optimistic robot, ~90% completeness can be achieved while rejecting ~90% of the candidate objects. The remaining candidates must be classified by human inspectors. We are able to classify lens candidates by eye at a rate of a few seconds per system, suggesting that a future 1000 square degree imaging survey containing 10^7 BRGs, and some 10^4 lenses, could be successfully, and reproducibly, searched in a modest amount of time. [Abridged]