Evidence for non-hydrostatic gas from the cluster X-ray to lensing mass ratio

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 r(2500), we obtain a ratio M(X)/M(L) = 1.03 +/- 0.07 which decreases to M(X)/M(L) = 0.78 +/- 0.09 at r(500). 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 non-thermal 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 f(gas) and find no correlation with M(L), an important result for techniques that aim to determine cosmological parameters using f(gas).