LoCuSS : testing hydrostatic equilibrium in galaxy clusters.

Abstract

We test the assumption of hydrostatic equilibrium in an X-ray luminosity selected sample of 50 galaxy clusters at 0.15 < z < 0.3 from the Local Cluster Substructure Survey (LoCuSS). Our weak-lensing measurements of M500 control systematic biases to sub-4 per cent, and our hydrostatic measurements of the same achieve excellent agreement between XMM–Newton and Chandra. The mean ratio of X-ray to lensing mass for these 50 clusters is βX=0.95±0.05βX=0.95±0.05, and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is βP=0.95±0.04βP=0.95±0.04. Based on a careful like-for-like analysis, we find that LoCuSS, the Canadian Cluster Comparison Project, and Weighing the Giants agree on βP≃0.9−0.95βP≃0.9−0.95 at 0.15 < z < 0.3. This small level of hydrostatic bias disagrees at ∼5σ with the level required to reconcile Planck cosmology results from the cosmic microwave background and galaxy cluster counts.