Tracing the non-thermal pressure and hydrostatic bias in galaxy clusters

Abstract

We present a modelization of the non-thermal pressure, PNT, and we apply it to the X-ray (and Sunayev-Zel’dovich) derived radial profiles of the X-COP galaxy clusters. We relate the amount of non-thermal pressure support to the hydrostatic bias, b, and speculate on how we can interpret this PNT in terms of the expected levels of turbulent velocity and magnetic fields. Current upper limits on the turbulent velocity in the intracluster plasma are used to build a distribution 𝒩(< b)−b, from which we infer that 50 per cent of local galaxy clusters should have b < 0.2 (b < 0.33 in 80 per cent of the population). The measured bias in the X-COP sample that includes relaxed massive nearby systems is 0.03 in 50% of the objects and 0.17 in 80% of them. All these values are below the amount of bias required to reconcile the observed cluster number count in the cosmological framework set from Planck.