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

We present a modelization of the non-thermal pressure, P N T , 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 P N T 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 .