We measured the velocity anisotropy profile, β(r), of different galaxy cluster member populations by analysing the stacked projected phase space of nine massive (M200c > 7 × 1014 M⊙) galaxy clusters at intermediate redshifts (0.18 MAMPOSSt method (parametric in β(r)) and the inversion of the Jeans equation (non-parametric in β(r)). The results from both techniques are found to be in agreement for any given cluster member population, and suggest that the orbital anisotropy in galaxy clusters grows from the centre (where β ≈ 0.2 − 0.4) to the virial radius (β ≳ 0.8), and it is similar for the different cluster-member populations. We also find an interesting dynamical feature emerging from the Jeans inversion results, that is, a sudden drop in β(r) at a distance of ∼250 kpc from the cluster centre. We provide robust anisotropy estimates from our exploration of a highly significant number of model combinations: 72 with MAMPOSSt (varying the mass, surface number density, β(r) model, and galaxy population) and 18 (varying total mass model and galaxy population) in the Jeans inversion. Such an extensive investigation of the velocity anisotropy profile in galaxy clusters is a wide basis for future studies of cluster dynamical masses and cluster cosmology in the era of large spectroscopic surveys.
Maraboli et al. (Mon,) studied this question.