Numerical simulations of x-ray clusters

We describe efforts to model the formation and evolution of X-ray clusters. After summarizing the current state of cluster observations, we describe the computational method used to model both the hot gas as well as the dark, collisionless component that observations imply. This code employs a higher-order accurate fluid-dynamics method for improved resolution and its accuracy is tested by a suite of tests.Using this method, we have modeled the large-scale distribution of clusters for both the Cold Dark Matter (CDM) and Cold plus Hot Dark Matter (CHDM) scenarios. We find that CDM produces too many clusters when compared to observations. The CHDM model seems to match the observed distribution, both in terms of temperature and luminosity, although the luminosity of a cluster is not well determined in these simulations, due to limited resolution.We compare the simulated clusters against analytic laws which provide scaling relations between the clusters' bulk properties and redshift. These are found to agree relatively well for the mass, velocity dispersion and temperature of a cluster. Although the luminosity does not agree as well, this is well explained by the fixed resolution of the simulations. These scaling relations are combined with a simple prescription for determining the number density as a function of mass to compute differential temperature and luminosity distributions including the effects of limited bandwidth and metallicity.We also examine the structure of cluster halos with larger resolution simulations, showing that shocks play an important role in cluster formation. Turbulent motions in the gas provide some support against gravity and decrease the temperature below that required by hydrostatic equilibrium. The temperature structure of the halos are directly compared to recent x-ray satellite observations.Finally, we briefly describe, and present first results from, a new Adaptive Mesh Refinement (AMR) cosmological simulation code. The algorithm has the benefits of Eulerian hydrodynamics techniques as well as adaptive resolution that follows the solution as it evolves. Results are presented from a simulation of an X-ray cluster that achieved a nominal spatial resolution (box length/cell size) of more than 8000, in selected regions.U of I OnlyETDs are only available to UIUC Users without author permissio