The cross-correlation between 3d cosmic shear and the integrated Sachs-Wolfe effect

TL;DR

This paper calculates the first cross-correlation between 3D cosmic shear and the integrated Sachs-Wolfe effect, showing how combining these signals enhances cosmological parameter constraints in upcoming surveys.

Contribution

It introduces a formalism to compute the full covariance of 3D cosmic shear and iSW signals, focusing on large scales to avoid non-linear uncertainties, and demonstrates the added value of their cross-correlation.

Findings

Combining shear and iSW signals reduces parameter errors by 10%.

Cross-correlation provides significant information gain on large scales.

Adding CMB data yields marginal improvements over shear and iSW combination.

Abstract

We present the first calculation of the cross-correlation between three-dimensional cosmic shear and the integrated Sachs-Wolfe (iSW) effect. Both signals are combined in a single formalism, which permits the computation of the full covariance matrix. In order to avoid the uncertainties presented by the non-linear evolution of the matter power spectrum and intrinsic alignments of galaxies, our analysis is restricted to large scales, i.e. multipoles below l=1000. We demonstrate in a Fisher analysis that this reduction compared to other studies of three-dimensional weak lensing extending to smaller scales is compensated by the information that is gained if the additional iSW signal and in particular its cross-correlation with lensing data are considered. Given the observational standards of upcoming weak lensing surveys like Euclid, marginal errors on cosmological parameters decrease by ten per cent compared to a cosmic shear experiment if both types of information are combined without a CMB prior. Once the constraining power of CMB data is added, the improvement becomes marginal.