Impact of intrinsic alignments on clustering constraints of the growth rate

TL;DR

This paper investigates how intrinsic galaxy alignments bias measurements of the Universe's growth rate from galaxy clustering data and explores mitigation strategies to improve the accuracy of these cosmological constraints.

Contribution

It quantifies the impact of intrinsic alignments on galaxy bias and growth rate estimates and evaluates mitigation methods for future high-precision clustering analyses.

Findings

Conservative analyses at low wave numbers are minimally affected by alignments.

Higher wave number analyses can be significantly biased without mitigation.

Using priors or combining probes can recover accurate growth rate constraints.

Abstract

Intrinsic alignments between galaxies and the large-scale structure contaminate galaxy clustering analyses and impact constraints on galaxy bias and the growth rate of structure in the Universe. This is the result of alignments inducing a selection effect on spectroscopic samples which is correlated with the large-scale structure. In this work, we quantify the biases on galaxy bias and the growth rate when alignments are neglected. We also examine different options for the mitigation of alignments by considering external priors on the effect and different probe combinations. We find that conservative analyses that restrict to $k_{\rm max}=0.1$ Mpc$^{-1}$ are not significantly affected. However, analyses that aim to go to higher wave numbers could evidence a significant contamination from alignments. In those cases, including a prior on alignment amplitude, or combining clustering with the position-intrinsic shape correlation of galaxies, can recover the same expected constraining power, or even inform bias and growth rate measurements.