The dark matter component of the Gaia radially anisotropic substructure
Nassim Bozorgnia, 18 May 2020
The local dark matter distribution is a crucial input in the analysis of results from dark matter direct detection experiments. The commonly adopted model for the dark matter halo of our Galaxy is the Standard Halo Model, in which the halo is assumed to be isothermal and the dark matter velocity distribution is an isotropic Maxwellian distribution. However, the true local dark matter distribution may be different from a Maxwellian distribution. State-of-the-art cosmoligical simulations together with recent astronomical data can provide us with important information on the local dark matter distribution.
One of the important discoveries made using the second data release from the Gaia satellite was a population of stars with high radial velocity anisotropy within approximately 10 kpc from the Sun. We have studied the properties of the dark matter component of the Gaia Radially Anisotropic Stellar Population (GRASP), using simulations of Milky Way-like galaxies from the Auriga project. We identified 10 Milky Way-like simulated halos, four of which had the GRASP component. We extracted the local dark matter density and velocity distribution of halos with and without the GRASP, and used them in the analysis of signals simulated in two future germanium and xenon direct detection experiments. We found that there is an anti-correlation between the fraction and anisotropy of the dark matter particles belonging to the GRASP in the Solar neighbourhood. A generalized Maxwellian distribution fits well the dark matter halo integrals of the simulated Milky Way-like halos with the GRASP. For low dark matter masses (below 10 GeV), direct detection exclusion limits for the halos with the GRASP slightly shift towards smaller dark matter masses compared to the Standard Halo Model.
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| Figure 1. |