Might we eventually understand the origin of the dark matter velocity anisotropy?

Understand

The density profile of simulated dark matter structures is fairly well-established, and several explanations for its characteristics have been put forward.

• In contrast, the radial variation of the velocity anisotropy has still not been explained.
• We suggest a very simple origin, based on the shapes of the velocity distributions functions, which are shown to differ between the radial and tangential directions.
• This allows us to derive a radial variation of the anisotropy profile which is in good agreement with both simulations and observations.