Characterization of subhalo structural properties and implications for dark matter annihilation signals

TL;DR

This paper uses N-body simulations to analyze subhalo structures in dark matter halos, refining models of their impact on dark matter annihilation signals by accounting for concentration differences and tidal stripping effects.

Contribution

It provides new detailed fits for subhalo structural properties and improves the substructure boost model for dark matter annihilation signals, including tidal stripping effects.

Findings

Subhalos are more concentrated than field halos.

Refined boost factors are 2-3 times higher than previous estimates.

Tidal stripping reduces boost factors by 20-30% for field halos and a few tens of percent for subhalos.

Abstract

A prediction of the standard LCDM cosmology is that dark matter (DM) halos are teeming with numerous self-bound substructure, or subhalos. The precise properties of these subhalos represent important probes of the underlying cosmological model. We use data from Via Lactea II and ELVIS N-body simulations to learn about the structure of subhalos with masses 1e6 - 1e11 Msun/h. Thanks to a superb subhalo statistics, we study subhalo properties as a function of distance to host halo center and subhalo mass, and provide a set of fits that accurately describe the subhalo structure. We also investigate the role of subhalos on the search for DM annihilation. Previous work has shown that subhalos are expected to boost the DM signal of their host halos significantly. Yet, these works traditionally assumed that subhalos exhibit similar structural properties than those of field halos, while it is known that subhalos are more concentrated. Building upon our N-body data analysis, we refine the substructure boost model of Sanchez-Conde & Prada (2014), and find boosts that are a factor 2-3 higher. We further refine the model to include unavoidable tidal stripping effects on the subhalo population. For field halos, this introduces a moderate 20-30% suppression. Yet, for subhalos like those hosting dwarf galaxy satellites, tidal stripping plays a critical role, the boost being at the level of a few tens of percent at most. We provide a parametrization of the boost for field halos that can be safely applied over a wide halo mass range.