Intrinsic alignments and 3d weak gravitational lensing

TL;DR

This paper integrates intrinsic galaxy alignments into 3d weak lensing formalism, deriving covariance matrices for different models and analyzing their impact relative to cosmic shear signals in surveys.

Contribution

It provides a consistent framework for including intrinsic alignments in 3d weak lensing analysis and compares their effects across models and survey types.

Findings

II-alignments dominate covariance at low redshift

II-alignments are smaller than lensing signal in Euclid-like surveys

Intrinsic alignments have distinct covariance matrix shapes, elongated along the diagonal

Abstract

In this paper we show how intrinsic alignments can be incorporated consistently in the formalism of 3d weak lensing. We use two different descriptions of the intrinsic galaxy ellipticities, the so-called linear and quadratic model, respectively. For both models we derive the covariance matrix of the intrinsic alignment signal (II-alignments) and GI-alignments (the cross correlation of intrinsic and lensing induced ellipticities). Evaluating the covariance matrices for the linear model numerically and comparing the results to the cosmic shear signal we find that for a low redshift survey the total covariance matrix is dominated by the contributions of the II-alignments. For a Euclid-like survey II-alignments still dominate over GI-alignments but they are more than one order of magnitude smaller than the lensing signal. The shape of the ellipticity covariance matrices is quite different in the k-k'-plane for cosmic shear on the one hand and intrinsic alignments on the other hand. In comparison to lensing both alignment types tend to be rather elongated along the diagonal k=k'. Moreover, for high multipoles (l ~ 100) intrinsic alignments are strongly concentrated along that diagonal.