Parameter likelihood of intrinsic ellipticity correlations

TL;DR

This paper analyzes the statistical properties of galaxy ellipticity alignments caused by angular momentum correlations, comparing intrinsic signals with gravitational lensing effects to assess their impact on cosmological parameter estimation.

Contribution

It introduces a model linking angular momentum to ellipticity correlations and evaluates their influence on cosmological measurements, highlighting differences from the linear alignment model.

Findings

Intrinsic ellipticity correlations produce non-Gaussian likelihoods.

Biases on dark energy parameters are small with the angular-momentum model.

Intrinsic ellipticities can be measured despite weak lensing contamination.

Abstract

Subject of this paper are the statistical properties of ellipticity alignments between galaxies evoked by their coupled angular momenta. Starting from physical angular momentum models, we bridge the gap towards ellipticity correlations, ellipticity spectra and derived quantities such as aperture moments, comparing the intrinsic signals with those generated by gravitational lensing, with the projected galaxy sample of EUCLID in mind. We investigate the dependence of intrinsic ellipticity correlations on cosmological parameters and show that intrinsic ellipticity correlations give rise to non-Gaussian likelihoods as a result of nonlinear functional dependencies. Comparing intrinsic ellipticity spectra to weak lensing spectra we quantify the magnitude of their contaminating effect on the estimation of cosmological parameters and find that biases on dark energy parameters are very small in an angular-momentum based model in contrast to the linear alignment model commonly used. Finally, we quantify whether intrinsic ellipticities can be measured in the presence of the much stronger weak lensing induced ellipticity correlations, if prior knowledge on a cosmological model is assumed.