Evidence for Non-Hydrostatic Gas from the Cluster X-ray to Lensing Mass Ratio

TL;DR

This study compares X-ray and lensing mass estimates of galaxy clusters, revealing a radial trend likely due to nonthermal pressure support, with implications for cosmological measurements.

Contribution

It provides the first uniform analysis of spatially resolved weak lensing and X-ray masses across multiple clusters, identifying a significant radial trend in mass ratios.

Findings

X-ray to lensing mass ratio decreases with radius

Correcting for correlated structure slightly reduces the trend

No correlation between gas fraction and lensing mass

Abstract

Using a uniform analysis procedure, we measure spatially resolved weak gravitational lensing and hydrostatic X-ray masses for a sample of 18 clusters of galaxies. We find a radial trend in the X-ray to lensing mass ratio: at r2500 we obtain a ratio MX/ML=1.03+/-0.07 which decreases to MX/ML=0.78+/-0.09 at r500. This difference is significant at 3 sigma once we account for correlations between the measurements. We show that correcting the lensing mass for excess correlated structure outside the virial radius slightly reduces, but does not eliminate this trend. An X-ray mass underestimate, perhaps due to nonthermal pressure support, can explain the residual trend. The trend is not correlated with the presence or absence of a cool core. We also examine the cluster gas fraction and find no correlation with ML, an important result for techniques that aim to determine cosmological parameters using the gas fraction.