Non-thermal pressure in galaxy clusters: what astrophysics can do for cosmology and vice versa

For cosmology, galaxy clusters are a unique tracer of structure growth at low redshift, thus ideal for constraining properties of the Dark Energy. However, the accuracy of galaxy clusters as a cosmological tracer is limited by our understanding of their physics. In particular, mass estimation of galaxy clusters are currently afflicted by a 'hydrostatic mass bias' which arises from the non-thermal pressure in the intracluster gas. We examine the physics of the injection and dissipation of the major contribution to the non-thermal pressure: the random motions in the intracluster gas. Interestingly, we find that the key is to have a cosmological perspective: to view galaxy clusters in the context of cosmic structure growth. We formulate our findings into an analytical model for non-thermal pressure. Its predictions match well with hydrodynamic simulations and observations. With the aid of this new model, we can correct the bias in the HSE masses to be well within 10% for samples of galaxy clusters of all dynamical states.