Journal Article

Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias

Elisabetta Semboloni, Ismael Tereno, Ludovic Van Waerbeke and Catherine Heymans

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 397, issue 2, pages 608-622
Published in print August 2009 | ISSN: 0035-8711
Published online July 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14926.x
Sources of contamination to weak lensing tomography: redshift-dependent shear measurement bias

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The current methods available to estimate gravitational shear from astronomical images of galaxies introduce systematic errors which can affect the accuracy of weak lensing cosmological constraints. We study the impact of KSB shape measurement bias on the cosmological interpretation of tomographic two-point weak lensing shear statistics.

We use a set of realistic image simulations produced by the Shear Testing Programme (STEP) collaboration to derive shape measurement bias as a function of redshift. We define biased two-point weak lensing statistics and perform a likelihood analysis for two fiducial surveys. We present a derivation of the covariance matrix for tomography in real space and a fitting formula to calibrate it for non-Gaussianity.

We find the biased aperture mass dispersion is reduced by ∼20 per cent at redshift ∼1, and has a shallower scaling with redshift. This effect, if ignored in data analyses, biases σ8 and w0 estimates by a few per cent. The power of tomography is significantly reduced when marginalizing over a range of realistic shape measurement biases. For a Canada-France-Hawaii Telescope Legacy Survey (CFHTLS)-Wide-like survey, [Ωm, σ8] confidence regions are degraded by a factor of 2, whereas for a Kilo-Degree Survey (KIDS)-like survey the factor is 3.5. Our results are strictly valid only for KSB methods, but they demonstrate the need to marginalize over a redshift-dependent shape measurement bias in all future cosmological analyses.

Keywords: gravitational lensing; cosmological parameters; large-scale structure of the Universe

Journal Article.  9547 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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