The Influence of Concentration and Dynamical State on Scatter in the Galaxy Cluster Mass-temperature Relation

Using a hydrodynamics plus N -body simulation of galaxy cluster formation within a large volume and mock Chandra X-ray observations, we study the form and evolution of the intrinsic scatter about the best-fit X-ray temperature-mass relation for clusters. We investigate the physical origin of the scatter by correlating it with quantities that are closely related to clusters’ formation and merging histories. We also examine the distribution of the scatter for merging and nonmerging populations, identified using halo merger trees derived from the simulation as well as X-ray substructure measures. We find a strong correlation between the scatter in the M − TX relation and the halo concentration, in the sense that more concentrated clusters tend to be cooler than clusters with similar masses. No bias is found between the merging and relaxed clusters, but merging clusters generally have greater scatter. The amount of scatter is smaller at z = 1 than at z = 0 for both populations. We show that the above trends can be explained by the properties of the distribution of halo concentrations. We also detect a signature of non-lognormality in the distribution of scatter for our simulated clusters both at z = 0 and at z = 1. We conclude that, when cooling-related effects are neglected, the intrinsic scatter in the M − TX relation is primarily driven by variations in halo concentrations, and only secondarily by departures from hydrostatic equilibrium due to cluster mergers. Subject headings: galaxies: clusters: general — hydrodynamics — intergalactic medium — X-rays: galaxies