LoCuSS: Testing hydrostatic equilibrium in galaxy clusters

TL;DR

This study tests the hydrostatic equilibrium assumption in galaxy clusters using X-ray and weak-lensing data, finding minimal bias that challenges previous cosmological discrepancy explanations.

Contribution

It provides precise weak-lensing mass measurements and compares them with X-ray and Planck estimates, revealing small hydrostatic bias in galaxy clusters.

Findings

Mean X-ray to lensing mass ratio is 0.95±0.05.

Planck mass estimates are consistent with lensing masses at 0.95±0.04.

Hydrostatic bias is too small to resolve Planck cosmology tensions.

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 $M_{500}$ 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 $\beta_{\rm X}=0.95\pm0.05$, and for the 44 clusters also detected by Planck, the mean ratio of Planck mass estimate to LoCuSS lensing mass is $\beta_{\rm P}=0.95\pm0.04$. Based on a careful like-for-like analysis, we find that LoCuSS, the Canadian Cluster Comparison Project (CCCP), and Weighing the Giants (WtG) agree on $\beta_{\rm P}\simeq0.9-0.95$ at $0.15<z<0.3$. This small level of hydrostatic bias disagrees at $\sim5\sigma$ with the level required to reconcile Planck cosmology results from the cosmic microwave background and galaxy cluster counts.