A New Method to Simulate Dark Matter-Baryon Interactions and Application to an Isolated Disk Galaxy

TL;DR

This paper introduces a novel simulation method for dark matter-baryon interactions, combining mean-field and Monte Carlo approaches, and demonstrates its impact on galaxy structure in a Milky Way-like model.

Contribution

A new hybrid simulation technique for DM-baryon interactions derived from the Boltzmann equation, implemented in GIZMO, enabling detailed galaxy evolution studies.

Findings

Strong central mass distribution changes for 1 barn cross section within 1 Gyr.

Interactions with hadronic cross sections can significantly alter galaxy features.

Method allows for high-fidelity simulations to explore observable galaxy effects.

Abstract

We report on a new method for incorporating interactions between dark matter (DM) and baryons in cosmological simulations, capable of handling the challenging regime in which the dark matter particle mass is comparable to or lighter than the baryon mass. The method hybridizes two distinct approaches: gas particles receive momentum and energy transfer according to a mean-field calculation while DM particles undergo Monte Carlo scatterings. These approaches are derived from the Boltzmann equation and shown to be statistically equivalent. We present an open-source implementation of this method in the simulation code GIZMO. As a first application, we investigate the effects of DM-baryon interactions on an isolated Milky Way-like disk galaxy for dark matter having twice the proton mass, which roughly maximizes the average energy transfer per collision. For cross sections of order 1 barn ($10^{-24}$ cm$^2$), these interactions cause strong changes to the mass distribution in the center of the galaxy in less than 1 Gyr, even when bar formation is suppressed by hand. For cross sections typical of hadronic interactions ($\lesssim 30$ mb), high-fidelity galaxy formation simulations will be needed to assess the effects on observable features of galaxies.