The dark matter component of the Gaia radially anisotropic substructure

TL;DR

This study investigates the dark matter component associated with a radially anisotropic stellar population in the Milky Way, using simulations to estimate local dark matter properties and implications for direct detection experiments.

Contribution

It provides the first analysis of the dark matter properties linked to the Gaia-identified stellar structure using realistic galaxy simulations.

Findings

Anti-correlation between dark matter fraction and orbital anisotropy.

Dark matter velocity distribution fits a generalized Maxwellian.

Detection limits shift for dark matter below 10 GeV in halos with the anisotropic population.

Abstract

We study the properties of the dark matter component of the radially anisotropic stellar population recently identified in the Gaia data, using magneto-hydrodynamical simulations of Milky Way-like halos from the Auriga project. We identify 10 simulated galaxies that approximately match the rotation curve and stellar mass of the Milky Way. Four of these have an anisotropic stellar population reminiscent of the Gaia structure. We find an anti-correlation between the dark matter mass fraction of this population in the Solar neighbourhood and its orbital anisotropy. We estimate the local dark matter density and velocity distribution for halos with and without the anisotropic stellar population, and use them to simulate the signals expected in future xenon and germanium direct detection experiments. We find that a generalized Maxwellian distribution fits the dark matter halo integrals of the Milky Way-like halos containing the radially anisotropic stellar population. For dark matter particle masses below approximately 10 GeV, direct detection exclusion limits for the simulated halos with the anisotropic stellar population show a mild shift towards smaller masses compared to the commonly adopted Standard Halo Model.