Image Analysis for Cosmology: Results from the GREAT10 Star Challenge

TL;DR

This paper reports on the results of the GREAT10 Star Challenge, a blind test for reconstructing spatially varying PSFs in astronomical images, crucial for accurate weak lensing measurements related to dark energy.

Contribution

It introduces the first public blind PSF reconstruction challenge and evaluates various methods' accuracy in modeling complex PSFs for cosmological image analysis.

Findings

Best methods achieved ~0.00025 ellipticity accuracy

Size squared was reconstructed with ~0.00074 precision

Modeling becomes more difficult with narrower PSFs and atmospheric turbulence

Abstract

We present the results from the first public blind PSF reconstruction challenge, the GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Star Challenge. Reconstruction of a spatially varying PSF, sparsely sampled by stars, at non-star positions is a critical part in the image analysis for weak lensing where inaccuracies in the modelled ellipticity and size-squared can impact the ability to measure the shapes of galaxies. This is of importance because weak lensing is a particularly sensitive probe of dark energy, and can be used to map the mass distribution of large scale structure. Participants in the challenge were presented with 27,500 stars over 1300 images subdivided into 26 sets, where in each set a category change was made in the type or spatial variation of the PSF. Thirty submissions were made by 9 teams. The best methods reconstructed the PSF with an accuracy of ~0.00025 in ellipticity and ~0.00074 in size squared. For a fixed pixel scale narrower PSFs were found to be more difficult to model than larger PSFs, and the PSF reconstruction was severely degraded with the inclusion of an atmospheric turbulence model (although this result is likely to be a strong function of the amplitude of the turbulence power spectrum).