An X‐Ray Size‐Temperature Relation for Galaxy Clusters: Observation and Simulation

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Abstract
We show that galaxy clusters conform to a tight relation between X-ray isophotal size RI and emission-weighted intracluster medium (ICM) temperature TX. The best-fit relation for 41 members of an X-ray flux-limited cluster sample is log RI = (0.93 ± 0.11) log (TX/6 keV) - (0.08 ± 0.01); intrinsic scatter in size about the relation is 15%, and for 30 clusters with TX > 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 TX. 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 Mvir and TX, providing the suggestion that a similar relation holds for observed clusters. We use the scatter in RI to estimate limits on the rms variation in ICM mass fraction δfICM at constant TX: δf/fICM ≤ 22% (≤14% for clusters with TX > 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.
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