Probing dipolar power asymmetry with galaxy clustering and intrinsic alignments

TL;DR

This paper explores how galaxy clustering and intrinsic alignments can be used to detect large-scale anisotropies in the universe, emphasizing the role of cross-correlations for robust constraints.

Contribution

It demonstrates that galaxy-IA cross-spectra significantly enhance the detection of primordial power asymmetry in upcoming surveys, with minimal bias impact.

Findings

IA alone offers limited anisotropy constraints

Galaxy-IA cross-spectrum can contribute up to half the clustering power

Bias marginalization has negligible effect on constraints

Abstract

We investigate the prospects for probing large-scale statistical anisotropy through galaxy clustering and intrinsic alignments (IA) in Stage IV galaxy surveys. Specifically, we consider a dipolar modulation in the primordial power spectrum and evaluate the Fisher information matrix using the two-point statistics of both the galaxy clustering and IA. Our analysis reveals that while IA alone provides limited improvement in constraining the anisotropy amplitude, the cross-spectrum between galaxy density and IA can contribute up to half the constraining power of galaxy clustering, especially for surveys with low galaxy bias and high number density of galaxies, such as Euclid. This demonstrates the potential of IA-clustering cross-correlations as a robust consistency check against systematics, and highlights the complementary roles of galaxy clustering and IA in constraining cosmic statistical anisotropy. We also show that marginalizing over galaxy bias and IA bias parameters has a negligible impact on the final constraint on the anisotropy amplitude.