Sources of contamination to weak lensing three-point statistics: constraints from N-body simulations |
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| Authors: | Elisabetta Semboloni Catherine Heymans Ludovic van Waerbeke Peter Schneider |
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| Institution: | Argelander-Institut für Astronomie, Auf dem Hügel 71, Bonn D-53121, Germany;University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada;Institut d'Astrophysique de Paris, 81bis Bd. Arago, F-75014 Paris, France |
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| Abstract: | We investigate the impact of the observed correlation between a galaxy's shape and its surrounding density field on the measurement of third-order weak lensing shear statistics. Using numerical simulations, we estimate the systematic error contribution to a measurement of the third-order moment of the aperture mass statistic (GGG) from three-point intrinsic ellipticity correlations (III), and the three-point coupling between the weak lensing shear experienced by distant galaxies and the shape of foreground galaxies (GGI and GII). We find that third-order weak lensing statistics are typically more strongly contaminated by these physical systematics compared to second-order shear measurements, contaminating the measured three-point signal for moderately deep surveys with a median redshift z m～ 0.7 by ～15 per cent. It has been shown that accurate photometric redshifts will be crucial to correct for this effect, once a model and the redshift dependence of the effect can be accurately constrained. To this end we provide redshift-dependent fitting functions to our results and propose a new tool for the observational study of intrinsic galaxy alignments. For a shallow survey with z m～ 0.4 we find III to be an order of magnitude larger than the expected cosmological GGG shear signal. Compared to the two-point intrinsic ellipticity correlation which is similar in amplitude to the two-point shear signal at these survey depths, third-order statistics therefore offer a promising new way to constrain models of intrinsic galaxy alignments. Early shallow data from the next generation of very wide weak lensing surveys will be optimal for this type of study. |
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| Keywords: | gravitational lensing cosmology: theory large-scale structure of Universe |
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