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

Rachel Mandelbaum, Barnaby Rowe, Robert Armstrong, Deborah Bard, Emmanuel Bertin, James Bosch, Dominique Boutigny, Frederic Courbin, William A. Dawson, Annamaria Donnarumma, Ian Fenech Conti, Raphaël Gavazzi, Marc Gentile, Mandeep S.S. Gill, David W. Hogg, Eric M. Huff, M. James Jee, Tomasz Kacprzak, Martin Kilbinger, Thibault KuntzerDustin Lang, Wentao Luo, Marisa C. March, Philip J. Marshall, Joshua E. Meyers, Lance Miller, Hironao Miyatake, Reiko Nakajima, Fred Maurice Ngolé Mboula, Guldariya Nurbaeva, Yuki Okura, Stéphane Paulin-Henriksson, Jason Rhodes, Michael D. Schneider, Huanyuan Shan, Erin S. Sheldon, Melanie Simet, Jean Luc Starck, Florent Sureau, Malte Tewes, Kristian Zarb Adami, Jun Zhang, Joe Zuntz

Research output: Contribution to journalArticlepeer-review

120 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)2963-3007
Number of pages45
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Jul 1 2015
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2015 The Authors.


  • Cosmology: observations
  • Gravitational lensing: weak
  • Methods: data analysis
  • Techniques: image processing


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