Self-Calibration for Three-Point Intrinsic Alignment Autocorrelations in Weak Lensing Surveys




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The weak lensing signal (cosmic shear) has been shown to be strongly contaminated by the various types of galaxy intrinsic alignment (IA) correlations, which poses a barrier to precision weak lensing measurements. The redshift dependence of the IA signal has been used at the two-point level to reduce this contamination by only measuring cross-correlations between large redshift bins, which significantly reduces the galaxy intrinsic ellipticity-intrinsic ellipticity (II) correlation. A self-calibration technique based on the redshift dependencies of the IA correlations has also been proposed as a means to remove the two-point IA contamination from the lensing signal. We explore here the redshift dependencies of the IA and lensing bispectra in order to propose a self-calibration of the IA autocorrelations at the three-point level (i.e. GGI, GII and III), which can be well understood without the assumption of any particular IA model. We find that future weak lensing surveys will be able to measure the distinctive IA redshift dependence over ranges of |Δ_ȥ^P| ≤ 0.2. Using conservative estimates of photo-ȥ accuracy, we describe the three-point self-calibration technique for the total IA signal, which can be accomplished through lensing tomography of photo-ȥ bin size ∼0.01. We find that the three-point self-calibration can function at the accuracy of the two-point technique with modest constraints in redshift separation. This allows the three-point IA autocorrelation self-calibration technique proposed here to significantly reduce the contamination of the IA contamination to the weak lensing bispectrum.



Cosmology, Dark energy (Astronomy), Tomography

"MI acknowledges that this material is based upon work supported in part by National Science Foundation under grant AST-1109667 and NASA under grant NNX09AJ55G, and that part of the calculations for this work have been performed on the Cosmology Computer Cluster funded by the Hoblitzelle Foundation"


© 2012 The Authors and Royal Astronomical Society.