Environmental dependence of ellipticity correlation functions of intrinsic alignments

Abstract

In this work we investigate the environmental dependence of the intrinsic ellipticity correlations in cosmic shear surveys. We use the quadratic and linear alignment model to describe the contributions by spiral and elliptical galaxies, respectively. The density field is in both cases described by a Gaussian random field and ellipticity correlation functions that are conditional on the environment of the galaxies are constructed by sampling random values for the tidal tensor and inertial tensor. The covariance of the Gaussian random process from which the tensor entries are drawn is decomposed by means of a spherical Fourier-Bessel transformation of the density field. The dependence on environment is modelled by the number of positive eigenvalues of the tidal tensor, which allows a differentiation between voids, sheets, filaments and superclusters. We find that elliptical galaxies align strongest in elongated structures such as sheets and filaments with an amplitude almost an order of magnitude higher compared to the alignment in clusters or voids. In contrast to this, spiral galaxies align equally strong in all environments. Cross-alignments between different environments are smaller than the respective auto-correlations subject to the Cauchy-Schwarz inequality which is an effective bound on their amplitude. Furthermore, we find misalignment between inertial and tidal tensor to be stronger in anisotropic regions compared to clusters or voids. While the imprint of weak lensing on galaxy ellipticities is agnostic about the environment, using environment information can help to distinguish between lensing and the intrinsic alignment signal.

Intrinsic and extrinsic correlations of galaxy shapes and sizes in weak lensing data

“…For simplicity, we work with a bias of unity without any dependence on mass or redshift, which is reasonable for low-mass galaxies in the relevant redshift range (Sheth & Tormen 1999). Modelling the statistics of the intrinsic alignment effects from a Gaussian random field as we do subsequently ignores that the galaxy shapes and sizes provide a measurement of the tidal field restricted to peak regions of the large-scale structure, which influences the statistics of tidal fields (Peacock & Heavens 1985;Schäfer & Merkel 2012), while the dependence of tidal fields on the environment should be reproduced (Forero-Romero et al 2014;Reischke & Schäfer 2019).…”

Galaxy Alignments with Surrounding Structure in the Sloan Digital Sky Survey

“…Thus, it is reasonable to assume some sort of alignment between the disk's angular momentum vector and the surrounding largescale structure. In addition, the outer regions of early-type galaxies will also be shaped by the tidal gravitational field of surrounding matter (Catelan et al 2001;Reischke & Schäfer 2019). The predictions of tidal torque theory can be extended into the nonlinear regime by analytic methods (Catelan et al 2001;Bridle & King 2007;Blazek et al 2015;Ebrahimian & Abolhasani 2022).…”