Dark matter phenomenology of high speed galaxy cluster collisions

TL;DR

This paper analyzes how weakly self-interacting dark matter affects mass distributions in high-speed galaxy cluster collisions, revealing measurable features like shells of scattered dark matter that could indicate dark matter self-interactions.

Contribution

It introduces a computational analysis showing that self-interacting dark matter creates observable features in collision mass distributions, especially in the halo tails, which are absent in purely gravitational models.

Findings

Up to 20% of collision mass can form shells at large angles.

Shell structures are indicative of dark matter self-interactions.

Features may explain observed dark matter rings in galaxy clusters.

Abstract

We perform a general computational analysis of possible post-collision mass distributions in high-speed galaxy cluster collisions in the presence of weakly self-interacting dark matter. Using this analysis, we show that weakly self-scattering dark matter can impart subtle yet measurable features in the mass distributions of colliding galaxy clusters even without significant disruptions to the dark matter halos of the colliding galaxy clusters themselves. Most profound such evidences are found to reside in the tails of dark matter halos' distributions, in the space between the colliding galaxy clusters. This feature appears in our simulations as shells of scattered dark matter expanding in alignment with the outgoing original galaxy clusters, contributing significant densities to projected mass distributions at large distances from collision centers and large scattering angles up to $90^\circ$. Our simulations indicate that as much as 20% of the total collision's mass may be deposited into such structures without noticeable disruptions to the main galaxy clusters. Such structures at large scattering angles are forbidden however in purely gravitational high-speed galaxy cluster collisions. Convincing identification of such structures in real colliding galaxy clusters would be a clear indication of the self-interacting nature of dark matter. Our findings may explain the dark matter ring feature recently found in the long-range reconstructions of the mass distribution of the colliding galaxy cluster CL0024+017.