An X-ray size-temperature relation for galaxy clusters: Observation and simulation

We show that galaxy clusters conform to a tight relation between X-ray isophotal size R-I and emission-weighted intracluster medium (ICM) temperature [T-X]. The best-fit relation for 41 members of an X-ray flux-limited cluster sample is log R-I = (0.93 +/- 0.11) log ([T-X]/6 keV)-(0.08 +/- 0.01); intrinsic scatter in size about the relation is 15%, and for 30 clusters with [T-X] > 4 keV, the scatter is reduced to 10%. The existence of the size-temperature (ST) relation indicates that the ICM structure is a well-behaved function of [T-X]. We use an ensemble of gasdynamic simulations to demonstrate that a cluster population experiencing present-epoch growth nevertheless conforms to an ST relation with scatter similar to that observed; the simulations also exhibit a tight relation between M-vir and [T-X], providing the suggestion that a similar relation holds for observed clusters. We use the scatter in R, to estimate limits on the rms variation in ICM mass fraction delta f(ICM) at constant [T-X]: delta f/f(ICM) less than or equal to 22% (less than or equal to 14% for clusters with [T-X] > 4 keV). It appears that a mechanism like feedback from galactic winds, which introduces systematic structural changes in the ICM, is required to reproduce the observed slope of the ST relation.