GREAT3 results – I. Systematic errors in shear estimation and the impact of real galaxy morphology

Abstract

We present first results from the third GRavitational lEnsing Accuracy Testing (GREAT3) challenge, the third in a sequence of challenges for testing methods of inferring weak gravitational lensing shear distortions from simulated galaxy images. GREAT3 was divided into experiments to test three specific questions, and included simulated space-and ground-based data with constant or cosmologically-varying shear fields. The simplest (control) experiment included parametric galaxies with a realistic distribution of signal-to-noise, size, and ellipticity, and a complex point spread function (PSF). The other experiments tested the additional impact of realistic galaxy morphology, multiple exposure imaging, and the uncertainty about a spatially-varying PSF; the last two questions will be explored in Paper II. The 24 participating teams competed to estimate lensing shears to within systematic error tolerances for upcoming Stage-IV dark energy surveys, making 1525 submissions overall. GREAT3 saw considerable variety and innovation in the types of methods applied. Several teams now meet or exceed the targets in many of the tests conducted (to within the statistical errors). We conclude that the presence of realistic galaxy morphology in simulations changes shear calibration biases by ∼ 1 per cent for a wide range of methods. Other effects such as truncation biases due to finite galaxy postage stamps, and the impact of galaxy type as measured by the Sérsic index, are quantified for the first time. Our results generalize previous studies regarding sensitivities to galaxy size and signal-to-noise, and to PSF properties such as seeing and defocus. Almost all methods' results support the simple model in which additive shear biases depend linearly on PSF ellipticity.

Two- and three-dimensional wide-field weak lensing mass maps from the Hyper Suprime-Cam Subaru Strategic Program S16A data

“…In short, the shapes of galaxies in the coadded i-band images are estimated using the re-Gaussianization method (Hirata & Seljak 2003), and are calibrated using simulated galaxy images that are similar to those used in GREAT3 (Mandelbaum et al 2015). The image simulation includes realistic HSC PSFs and is carefully designed to reproduce the observed distribution of galaxy properties remarkably well, which allows a reliable estimate shear calibration and additive biases (see Mandelbaum et al, in prep.).…”

Radio weak lensing shear measurement in the visibility domain – I. Methodology

“…The state-of-the-art in optical lensing measurements fits model surface brightness distributions to galaxies and combine these measurements to form an estimate of the cosmic shear. For a summary, see Mandelbaum et al (2015). Radio interferometers do not provide directly images of the observed sky, they measure visibility data instead, that basically are the Fourier transform of the sky image at sampled points in the Fourier (uv) domain.…”

Testing PSF Interpolation in Weak Lensing with Real Data

“…, Kaiser et al (1995)), while most of other more recently developed methods need the whole reconstructed PSF image (see, e.g. , Kitching et al (2012); Mandelbaum et al (2015)). Therefore, the standard for judging the quality of PSF reconstruction is not quite unique, and its influence on shear measurement is better discussed within a specific shear measurement method.…”