Ultra-fine dark matter structure in the Solar neighbourhood

TL;DR

This paper models the ultra-fine dark matter structure in the Solar neighborhood using a merger tree approach, revealing that the local velocity distribution is mostly smooth except for rare merger events that could produce detectable features.

Contribution

It introduces a novel application of a merger tree-based method to analyze ultra-fine dark matter structures relevant for direct detection experiments.

Findings

Velocity distribution is mostly smooth due to multiple mergers.

A significant merger can create detectable features in the velocity distribution.

Current experiments might detect signatures from rare, large mergers.

Abstract

The direct detection of dark matter on Earth depends crucially on its density and its velocity distribution on a milliparsec scale. Conventional N-body simulations are unable to access this scale, making the development of other approaches necessary. In this paper, we apply the method developed in Fantin et al. 2008 to a cosmologically-based merger tree, transforming it into a useful instrument to reproduce and analyse the merger history of a Milky Way-like system. The aim of the model is to investigate the implications of any ultra-fine structure for the current and next generation of directional dark matter detectors. We find that the velocity distribution of a Milky Way-like Galaxy is almost smooth, due to the overlap of many streams of particles generated by multiple mergers. Only the merger of a 10^10 Msun analyse can generate significant features in the ultra-local velocity distribution, detectable at the resolution attainable by current experiments.