Triaxiality and non-thermal gas pressure in Abell 1689

Abstract

Clusters of galaxies are uniquely important cosmological probes of the evolution of the large-scale structure, whose diagnostic power depends quite significantly on the ability to reliably determine their masses. Clusters are typically modelled as spherical systems whose intracluster gas is in strict hydrostatic equilibrium (i.e. the equilibrium gas pressure is provided entirely by thermal pressure), with the gravitational field dominated by dark matter, assumptions that are only rough approximations. In fact, numerical simulations indicate that galaxy clusters are typically triaxial, rather than spherical, and that turbulent gas motions (induced during hierarchical merger events) provide an appreciable pressure component. Extending our previous work, we present results of a joint analysis of X-ray, weak- and strong-lensing measurements of Abell 1689. The quality of the data allows us to determine both the triaxial shape of the cluster and the level of non-thermal pressure that is required if the intracluster gas is in hydrostatic equilibrium. We find that the dark matter axial ratios are 1.24 ± 0.13 and 2.02 ± 0.01 on the plane of the sky and along the line of sight, respectively, and that about 20 per cent of the pressure is non-thermal. Our treatment demonstrates that the dynamical properties of clusters can be determined in a (mostly) bias-free way, enhancing the use of clusters as more precise cosmological probes. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.