Triaxiality and non-thermal gas pressure in Abell 1689
  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 modeled 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 axis 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% 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.
