Quantifying the heart of darkness with GHALO - a multi-billion particle simulation of our galactic halo

TL;DR

This paper presents ultra-high-resolution simulations of a galactic dark matter halo, analyzing its density profile, shape, and phase-space structure, revealing new fitting functions and convergence properties.

Contribution

It introduces a new two-parameter density profile fitting function and provides detailed analysis of resolution effects on halo properties.

Findings

Density profile measured to 120 pc with specific slopes

New fitting function with linearly varying density gradient

Convergence scales as N^(-1/3), halo shape becomes more spherical at higher resolution

Abstract

We perform a series of simulations of a Galactic mass dark matter halo at different resolutions, our largest uses over three billion particles and has a mass resolution of 1000 M_sun. We quantify the structural properties of the inner dark matter distribution and study how they depend on numerical resolution. We can measure the density profile to a distance of 120 pc (0.05% of R_vir) where the logarithmic slope is -0.8 and -1.4 at (0.5% of R_vir). We propose a new two parameter fitting function that has a linearly varying logarithmic density gradient which fits the GHALO and VL2 density profiles extremely well. Convergence in the density profile and the halo shape scales as N^(-1/3), but the shape converges at a radius three times larger at which point the halo becomes more spherical due to numerical resolution. The six dimensional phase-space profile is dominated by the presence of the substructures and does not follow a power law, except in the smooth under-resolved inner few kpc.