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The shear testing programme 2 : factors affecting high-precision weak-lensing analyses.

Massey, R. and Heymans, C. and Bergé, J. and Bernstein, G. and Bridle, S. and Clowe, D. and Dahle, H. and Ellis, R. and Erben, T. and Hetterscheidt, M. and High, F.W. and Hirata, C. and Hoekstra, H. and Hudelot, P. and Jarvis, M. and Johnston, D. and Kuijken, K. and Margoniner, V. and Mandelbaum, R. and Mellier, Y. and Nakajima, R. and Paulin-Henriksson, S. and Peeples, M. and Roat, C. and Refregier, A. and Rhodes, J. and Schrabback, T. and Schirmer, M. and Seljak, U. and Semboloni, E. and Van Waerbeke, L. (2007) 'The shear testing programme 2 : factors affecting high-precision weak-lensing analyses.', Monthly notices of the Royal Astronomical Society., 376 (1). pp. 13-38.


The Shear Testing Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak-lensing measurement, in preparation for the next generation of wide-field surveys. We review 16 current and emerging shear-measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known shear signal. We determine the common features of algorithms that most successfully recover the input parameters. A desirable goal would be the combination of their best elements into one ultimate shear-measurement method. In this analysis, we achieve previously unattained discriminatory precision via a combination of more extensive simulations and pairs of galaxy images that have been rotated with respect to each other. That removes the otherwise overwhelming noise from their intrinsic ellipticities. Finally, the robustness of our simulation approach is confirmed by testing the relative calibration of methods on real data. Weak-lensing measurements have improved since the first STEP paper. Several methods now consistently achieve better than 2 per cent precision, and are still being developed. However, we can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative shear calibration bias: not least because this cannot be internally calibrated with real data. We determine which galaxy populations are responsible for bias and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. The simulated point spread functions are not allowed to vary spatially, to avoid additional confusion from interpolation errors. We have isolated several previously unrecognized aspects of galaxy shape measurement, in which focused development could provide further progress towards the sub-per cent level of precision desired for future surveys. These areas include the suitable treatment of image pixellization and galaxy morphology evolution. Ignoring the former effect affects the measurement of shear in different directions, leading to an overall underestimation of shear and hence the amplitude of the matter power spectrum. Ignoring the second effect could affect the calibration of shear estimators as a function of galaxy redshift, and the evolution of the lensing signal, which will be vital to measure parameters including the dark energy equation of state.

Item Type:Article
Keywords:Gravitational lensing, Methods: data analysis, Cosmology: observations.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2007 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Record Created:20 Feb 2015 10:05
Last Modified:09 Mar 2015 11:36

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