Breaking cosmological degeneracies in galaxy cluster surveys with a physical model of cluster structure

It has been shown that in an idealized galaxy cluster survey, containing 10,000 clusters, statistical errors on dark energy and other cosmological parameters would be at the percent level. Furthermore, through self-calibration, parameters describing the mass-observable relation and cosmology could be simultaneously determined, although at a loss in accuracy by about an order of magnitude. Here we examine an alternative approach to self-calibration, in which a parameterized ab initio physical model is used to compute theoretical mass-observable relations from the cluster structure. As an example, we use a modified-entropy (preheating) model of the intracluster medium, with the history and magnitude of entropy injection as unknown input parameters. Using a Fisher matrix approach, we evaluate the expected simultaneous statistical errors on cosmological and cluster model parameters. We find that compared to a phenomenological parameterization of the mass-observable relation, our physical model yields significantly tighter constraints in both surveys and offers substantially improved synergy when the two surveys are combined. In a mock X-ray survey, we find statistical errors on the dark energy equation of state are a factor of 2 tighter than the phenomenological model, with Delta w(0) similar to 0.08 and its evolution, Delta w(a) equivalent to -Delta dw/da similar to 0.23, with corresponding errors of Delta w(0) similar to 0.06 and Delta w(a) similar to 0.17 from a mock Sunyaev-Zel'dovich (SZ) survey, both with N-cl similar to 2.2 x 10(4) clusters, while simultaneously constraining cluster model parameters to less than or similar to 10%. When the two surveys are combined, the constraints tighten to Delta w(0) similar to 0.03 and Delta w(a) similar to 0.1, a 40% improvement over adding the individual experiment errors in quadrature and a factor of 2 improvement over the phenomenological model. This suggests that parameterized physical models of cluster structure would be useful when extracting cosmological constraints from SZ and X-ray cluster surveys.