Results of the GREAT08 Challenge★: an image analysis competition for cosmological lensing

Abstract

We present the results of the GREAT08 Challenge, a blind analysis challenge\nto infer weak gravitational lensing shear distortions from images. The primary\ngoal was to stimulate new ideas by presenting the problem to researchers\noutside the shear measurement community. Six GREAT08 Team methods were\npresented at the launch of the Challenge and five additional groups submitted\nresults during the 6 month competition. Participants analyzed 30 million\nsimulated galaxies with a range in signal to noise ratio, point-spread function\nellipticity, galaxy size, and galaxy type. The large quantity of simulations\nallowed shear measurement methods to be assessed at a level of accuracy\nsuitable for currently planned future cosmic shear observations for the first\ntime. Different methods perform well in different parts of simulation parameter\nspace and come close to the target level of accuracy in several of these. A\nnumber of fresh ideas have emerged as a result of the Challenge including a\nre-examination of the process of combining information from different galaxies,\nwhich reduces the dependence on realistic galaxy modelling. The image\nsimulations will become increasingly sophisticated in future GREAT challenges,\nmeanwhile the GREAT08 simulations remain as a benchmark for additional\ndevelopments in shear measurement algorithms.\n