MODELS OF GALAXY CLUSTERS WITH HEATING AND COOLING:
EXPLAINING THE GLOBAL AND STRUCTURAL X-RAY
PROPERTIES OF CLUSTERS

Failure of the "standard model" at accounting for the X-ray properties of galaxy clusters has led to an increased interest in understanding the role of non-gravitational processes such as heating or cooling. Both heating-only and cooling-only models can account for the mean global properties of the clusters. Cooling-only models, however, predict too high a fraction of cold gas and stars, and the heating-only models cannot account for the variations in the structural properties of the ICM. Models that marry the two, however, fare remarkably well. Not only are they able to account for the observed L-T, M-L relations and other such global trends, but also offer an explanation for the observed scatter in such relationships. Additionally, the models also provide a basis for understanding the broad diversity in the internal properties of the galaxy clusters and within this context, predict that there ought to be tight correlation between a cluster's central entropy and its core size. Preliminary examination of the observations indicates just
such a correlation.