A New Robust Low-Scatter X-Ray Mass Indicator for Clusters of Galaxies

Abstract

We present a comparison of X-ray proxies for the total cluster mass, M_(500), including the spectral temperature (T_X), gas mass measured within r_(500) (M_(g,500)), and the new proxy, Y_X, which is a simple product of T_X and M_(g,500) and is related to the total thermal energy of the ICM. We use mock Chandra images constructed for a sample of clusters simulated with the Eulerian N-body+gasdynamics adaptive mesh refinement ART code in the concordance ΛCDM cosmology. The simulations achieve high spatial and mass resolution and include radiative cooling, star formation, and other processes accompanying galaxy formation. Our analysis shows that simulated clusters exhibit a high degree of regularity and tight correlations between the considered observables and total mass. The normalizations of the M_(500)-T_X, M_(g,500)-T_X, and M_(500)-Y_X relations agree to better than ≈10%-15% with the current observational measurements of these relations. Our results show that Y_X is the best mass proxy with a remarkably low scatter of only ≈5%-7% in M500 for a fixed Y_X, at both low and high redshifts and regardless of whether clusters are relaxed or not. In addition, we show that redshift evolution of the Y_(X)-M_(500) relation is close to the self-similar prediction, which makes Y_X a very attractive mass indicator for measurements of the cluster mass function from X-ray-selected samples.