Bayesian galaxy shape measurement for weak lensing surveys – III. Application to the Canada–France–Hawaii Telescope Lensing Survey

Creators: Miller, L.; Heymans, C.; Kitching, T. D.; van Waerbeke, L.; Erben, T.; Hildebrandt, H.; Hoekstra, H.; Mellier, Y.; Rowe, B. P. T.; Coupon, J.; Dietrich, J. P.; Fu, L.; Harnois-Déraps, J.; Hudson, M. J.; Kilbinger, M.; Kuijken, K.; Schrabback, T.; Semboloni, E.; Vafaei, S.; Velander, M.

Abstract

A likelihood-based method for measuring weak gravitational lensing shear in deep galaxy surveys is described and applied to the Canada–France–Hawaii Telescope (CFHT) Lensing Survey (CFHTLenS). CFHTLenS comprises 154 deg^2 of multi-colour optical data from the CFHT Legacy Survey, with lensing measurements being made in the i′ band to a depth i′_(AB) < 24.7, for galaxies with signal-to-noise ratio ν_(SN) ≳ 10. The method is based on the lensfit algorithm described in earlier papers, but here we describe a full analysis pipeline that takes into account the properties of real surveys. The method creates pixel-based models of the varying point spread function (PSF) in individual image exposures. It fits PSF-convolved two-component (disc plus bulge) models to measure the ellipticity of each galaxy, with Bayesian marginalization over model nuisance parameters of galaxy position, size, brightness and bulge fraction. The method allows optimal joint measurement of multiple, dithered image exposures, taking into account imaging distortion and the alignment of the multiple measurements. We discuss the effects of noise bias on the likelihood distribution of galaxy ellipticity. Two sets of image simulations that mirror the observed properties of CFHTLenS have been created to establish the method's accuracy and to derive an empirical correction for the effects of noise bias.

Additional Information

© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2012 November 20. Received 2012 November 20; in original form 2012 July 31. First published online: January 14, 2013. This work is based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the CFHT which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. We thank the CFHT staff for successfully conducting the CFHTLS observations and in particular Jean-Charles Cuillandre and Eugene Magnier for the continuous improvement of the instrument calibration and the Elixir detrended data that we used. We also thank TERAPIX for the individual exposures quality assessment and validation during the CFHTLS data acquisition period, and Emmanuel Bertin for developing some of the software used in this study. CFHTLenS data processing was made possible thanks to significant computing support from the NSERC Research Tools and Instruments grant program, and to HPC specialist Ovidiu Toader. CH acknowledges support from the European Research Council under the EC FP7 grant number 240185. TDK acknowledges support from a Royal Society University Research Fellowship. LVW acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institute for Advanced Research (CIfAR, Cosmology and Gravity program). TE is supported by the Deutsche Forschungsgemeinschaft through project ER 327/3-1 and the Transregional Collaborative Research Centre TR 33 – 'The Dark Universe'. H. Hildebrandt is supported by the Marie Curie IOF 252760 and by a CITA National Fellowship. H. Hoekstra acknowledges support from Marie Curie IRG grant 230924, the Netherlands Organization for Scientific Research (NWO) grant number 639.042.814 and from the European Research Council under the EC FP7 grant number 279396. YM acknowledges support from CNRS/INSU (Institut National des Sciences de l'Univers) and the Programme National Galaxies et Cosmologie (PNCG). JPD was supported by NSF grant AST 0807304. LF acknowledges support from NSFC grants 11103012 and 10878003, Innovation Program 12ZZ134 and Chen Guang project 10CG46 of SMEC, STCSM grant 11290706600 and Pujiang Program 12PJ1406700. MJH acknowledges support from the Natural Sciences and Engineering Research Council of Canada (NSERC). TS acknowledges support from NSF through grant AST-0444059-001, SAO through grant GO0-11147A, and NWO. MV acknowledges support from the Netherlands Organization for Scientific Research (NWO) and from the Beecroft Institute for Particle Astrophysics and Cosmology. The N-body simulations used in this analysis were performed on the TCS supercomputer at the SciNet HPC Consortium. SciNet is funded by: the Canada Foundation for Innovation under the auspices of Compute Canada; the Government of Ontario; Ontario Research Fund – Research Excellence; and the University of Toronto. We thank Sree Balan, Sarah Bridle and Emmanuel Bertin for the simulation code used in this analysis. Author Contributions: All authors contributed to the development and writing of this paper. The authorship list reflects the lead authors of this paper (LM, CH, TDK, LVW) followed by two alphabetical groups. The first alphabetical group includes key contributors to the science analysis and interpretation in this paper, the founding core team and those whose long-term significant effort produced the final CFHTLenS data product. The second group covers members of the CFHTLenS team who made a significant contribution to the project and/or this paper. CH and LVW co-led the CFHTLenS collaboration.

Attached Files

Published - MNRAS-2013-Miller-2858-80.pdf

Files

MNRAS-2013-Miller-2858-80.pdf

Files (4.6 MB)

Name	Size	Download all
MNRAS-2013-Miller-2858-80.pdf md5:3f282b08f8aaee670930fef1bca01ec6	4.6 MB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes