The Dynamical Response of Dark Matter to Galaxy Evolution Affects Direct-Detection Experiments

TL;DR

This paper uses n-body simulations to show how dark matter dynamics in barred galaxies, especially the Milky Way, significantly influence direct-detection experiment rates by creating density and kinematic wakes that enhance or modulate signals.

Contribution

The study demonstrates that dark matter responses to galaxy evolution, such as shadow bars and wakes, can increase detection rates by over 30%, surpassing previous models.

Findings

Dark matter density in the disk plane increases by over 30%.

Detection rates can be more than doubled due to dark matter wakes.

Annual modulation signals are affected by galaxy dynamics.

Abstract

Over a handful of rotation periods, dynamical processes in barred galaxies induce non-axisymmetric structure in dark matter halos. Using n-body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark-matter component, a shadow bar, and a strong response wake in the dark-matter distribution that affects the predicted dark-matter detection rates for current experiments. The presence of a baryonic disk together with well-known dynamical processes (e.g. spiral structure and bar instabilities) increase the dark matter density in the disk plane. We find that the magnitude of the combined stellar and shadow bar evolution, when isolated from the effect of the axisymmetric gravitational potential of the disk, accounts for >30% of this overall increase in disk-plane density. This is significantly larger that of previously claimed deviations from the standard halo model. The dark-matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, especially for the experiments with higher $v_{min}$. These astrophysical features increase the detection rate by more than a factor of two when compared to the standard halo model and by a factor of ten for experiments with high minimum recoil energy thresholds. These same features increase (decrease) the annual modulation for low (high) minimum recoil energy experiments. We present physical arguments for why these dynamics are generic for barred galaxies such as the Milky Way rather than contingent on a specific galaxy model.