The Graininess of Dark Matter Haloes

Abstract

We use the recently completed one billion particle Via Lactea II LambdaCDM simulation to investigate local properties like density, mean velocity, velocity dispersion, anisotropy, orientation and shape of the velocity dispersion ellipsoid, as well as structure in velocity space of dark matter haloes. We show that at the same radial distance from the halo centre, these properties can deviate by orders of magnitude from the canonical, spherically averaged values, a variation that can only be partly explained by triaxiality and the presence of subhaloes. The mass density appears smooth in the central relaxed regions but spans four orders of magnitude in the outskirts, both because of the presence of subhaloes as well as of underdense regions and holes in the matter distribution. In the inner regions the local velocity dispersion ellipsoid is aligned with the shape ellipsoid of the halo. This is not true in the outer parts where the orientation becomes more isotropic. The clumpy structure in local velocity space of the outer halo can not be well described by a smooth multivariate normal distribution. Via Lactea II also shows the presence of cold streams made visible by their high 6D phase space density. Generally, the structure of dark matter haloes shows a high degree of graininess in phase space that cannot be described by a smooth distribution function.

22 pages, 14 figures, 1 table, accepted for publication by MNRAS

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• Inferring the gravitational potential of the Milky Way with a few precisely measured stars
• Modeling dark matter subhalos in a constrained galaxy: Global mass and boosted annihilation profiles
• WIMPs during Reheating
• Simulating tidal streams in a high resolution dark matter halo
• Simulations of Recoiling Massive Black Holes in the Via Lactea Halo
• The behaviour of shape and velocity anisotropy in dark matter haloes
• Systematic uncertainties from halo asphericity in dark matter searches
• Shining Primordial Black Holes
• Dark Matter Halos from the Inside Out
• Future sensitivity of neutrino telescopes to dark matter annihilations from the cosmic diffuse neutrino signal
• Asymmetric velocity anisotropies in remnants of collisionless mergers
• Enhancing Direct Detection of Higgsino Dark Matter