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

We present comparison of X-ray proxies for the total cluster mass, includingthe spectral temperature (Tx), gas mass measured within r500 (Mg), and the newproxy, Yx, which is a simple product of Tx and Mg and is related to the totalthermal energy of the ICM. We use mock Chandra images constructed for a sampleof clusters simulated with the eulerian N-body+gasdynamics adaptive meshrefinement ART code in the concordance LCDM cosmology. The simulations achievehigh spatial and mass resolution and include radiative cooling, star formation,and other processes accompanying galaxy formation. Our analysis shows thatsimulated clusters exhibit a high degree of regularity and tight correlationsbetween the considered observables and total mass. The normalizations of theM-Tx, Mg-Tx, and M-Yx relations agree to better than 10-15% with the currentobservational measurements of these relations. Our results show that Yx is thebest mass proxy with a remarkably low scatter of only ~5-7% in M500 for a fixedYx, at both low and high redshifts and regardless of whether clusters arerelaxed or not. In addition, we show that redshift evolution of the Yx-M500relation is close to the self-similar prediction, which makes Yx a veryattractive mass indicator for measurements of the cluster mass function fromX-ray selected samples.Comment: submitted to ApJ; 9 pages, 6 figures, uses emulateap