Anisotropic q-Gaussian velocity distributions in LambdaCDM halos

Understand

The velocity distribution function (VDF) of dark matter (DM) halos in $\Lambda$CDM dissipationless cosmological simulations, which must be non-separable in its radial and tangential components, is still poorly known.

• We present the first single-parameter, non-separable, anisotropic model for the VDF in $\Lambda$CDM halos, built from an isotropic $q$-Gaussian (Tsallis) VDF of the isotropic set of dimensionless spherical velocity components (after subtraction of streaming motions), normalized by the respective velocity dispersions.
• We test our VDF on 90 cluster-mass halos of a dissipationless cosmological simulation.
• Beyond the virial radius, $r_{\rm vir}$, our model VDF adequately reproduces that measured in the simulated halos, but no $q$-Gaussian model can adequately represent the VDF within $r_{\rm vir}$, as the speed distribution function is then flatter-topped than any $q$-Gaussian can allow.