A dark matter disc in three cosmological simulations of Milky Way mass galaxies

TL;DR

This study uses cosmological hydrodynamics simulations to show that baryonic matter creates a dark matter disc in Milky Way-like galaxies, significantly impacting dark matter detection signals.

Contribution

First to incorporate baryonic physics self-consistently in simulations, revealing the formation of a dark matter disc affecting local dark matter properties.

Findings

Dark matter disc contributes 0.25-1.5 times the local halo density.

Dark disc has low rotation lag, enhancing WIMP detection signals.

Dark disc influences annual modulation and recoil energy variations.

Abstract

Making robust predictions for the phase space distribution of dark matter at the solar neighbourhood is vital for dark matter direct detection experiments. To date, almost all such predictions have been based on simulations that model the dark matter alone. Here, we use three cosmological hydrodynamics simulations of bright, disc dominated galaxies to include the effects of baryonic matter self-consistently for the first time. We find that the addition of baryonic physics drastically alters the dark matter profile in the vicinity of the Solar neighbourhood. A stellar/gas disc, already in place at high redshift, causes merging satellites to be dragged preferentially towards the disc plane where they are torn apart by tides. This results in an accreted dark matter disc that contributes ~0.25 - 1.5 times the non-rotating halo density at the solar position. The dark disc, unlike dark matter streams, is an equilibrium structure that must exist in disc galaxies that form in a hierarchical cosmology. Its low rotation lag with respect to the Earth significantly boosts WIMP capture in the Earth and Sun, boosts the annual modulation signal, and leads to distinct variations in the flux as a function of recoil energy that allow the WIMP mass to be determined.