The impact of Self-Interacting Dark Matter on the Intrinsic Alignments of Galaxies

TL;DR

This study explores how self-interacting dark matter influences galaxy shape correlations, revealing a significant suppression of intrinsic alignments that could be detected in future surveys, thus providing insights into dark matter properties.

Contribution

It demonstrates that dark matter self-interactions cause a measurable, scale-dependent suppression in galaxy intrinsic alignments, distinguishable from baryonic effects.

Findings

Self-interactions suppress intrinsic alignments by up to 50%.

The suppression is mass-dependent and scale-dependent.

Impact is detectable with upcoming all-sky surveys.

Abstract

The formation and evolution of galaxies is known to be sensitive to tidal processes leading to intrinsic correlations between their shapes and orientations. Such correlations can be measured to high significance today, suggesting that cosmological information can be extracted from them. Among the most pressing questions in particle physics and cosmology is the nature of dark matter. If dark matter is self-interacting, it can leave an imprint on galaxy shapes. In this work, we investigate whether self-interactions can produce a long-lasting imprint on intrinsic galaxy shape correlations. We investigate this observable at low redshift ($z<0.4$) using a state-of-the-art suite of cosmological hydro-dynamical simulations where the dark matter model is varied. We find that dark matter self-interactions induce a mass dependent suppression in the intrinsic alignment signal by up to 50\% out to ten's of mega-parsecs, showing that self-interactions can impact structure outside the very core of clusters. We find evidence that self-interactions have a scale-dependent impact on the intrinsic alignment signal that is sufficiently different from signatures introduced by differing baryonic physics prescriptions, suggesting that it is detectable with up-coming all-sky surveys.