Smoothed Particle Inference : a Kilo - Parametric Method for X - Ray Galaxy Cluster Modeling

We propose an ambitious new method that models the intracluster medium in clusters of galaxies as a set of X-ray emitting smoothed particles of plasma. Each smoothed particle is described by a handful of parameters including temperature, location, size, and elemental abundances. Hundreds to thousands of these particles are used to construct a model cluster of galaxies, with the appropriate complexity estimated from the data quality. This model is then compared iteratively with X-ray data in the form of adaptively binned photon lists via a two-sample likelihood statistic and iterated via Markov Chain Monte Carlo. The complex cluster model is propagated through the X-ray instrument response using direct sampling Monte Carlo methods. Using this approach the method can reproduce many of the features observed in the X-ray emission in a less assumption-dependent way that traditional analyses, and it allows for a more detailed characterization of the density, temperature, and metal abundance structure of clusters. Multi-instrument X-ray analyses and simultaneous X-ray, Sunyaev-Zeldovich (SZ), and lensing analyses are a straightforward extension of this methodology. Significant challenges still exist in understanding the degeneracy in these models and the statistical noise induced by the complexity of the models. There are a large class of data analysis problems in astrophysics involving a model of a source that has a spectrum that varies spatially on the sky. In the case of the X-ray emission from clusters of galaxies, where the individual photon energies are recorded, the problem is especially prominent. In fact, much of the recent work in the X-ray analysis of clusters of galaxies has had the aim of obtaining a complete description of the density and temperature structure of the intracluster medium. The X-ray emission from clusters of galaxies has been recently shown, using observations with the Chandra and XMM-Newton telescopes, to have a very complex distribution. In general, the surface brightness lacks circular symmetry. For example, cold fronts, or cluster gas that " sloshing " relative to the dark matter gravitational potential , is a significant perturbation from a spherically-symmetric gas distribution (Markevitch et al. 2000). " Radio bubbles " , which are displacements of cluster gas by rel-ativistic radio-emitting plasma, have complex morphologies and vary from cluster to cluster. Sanders et al. (2004) have identified a " swirl " in the temperature structure of the Perseus cluster possibly due to rotation of the cluster gas. There may also be ripples or waves …