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

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 M 500 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.