Abstract. A new, combined N-body and 3D hydrodynamic simulation algorithm is used to study the dynamics of the intracluster medium (ICM) in rich clusters of galaxies. Results of a program to study an ensemble of clusters covering a range of cluster richness within the framework of a cold dark matter (CDM) dominated universe are presented. Comparison with observations for both individual cluster characteristics and properties of the ensemble is emphasized. Predictions arising from the numerical models will be discussed and directions for future work in this area outlined.

INTRODUCTION

The intergalactic space in rich clusters of galaxies is permeated by a hot, ionized plasma which emits a continuum of X-rays generated by the scattering of energetic electrons off protons and ions. This thermal bremsstrahlung emission is observed to distances R ∼ 1 Mpc and spectral fits indicate temperatures T ∼ 108 K, so if the gas is confined by the gravitational potential of the cluster the binding mass must be of order M≃G−1(kT/μmp)R ∼ 3 × 1014 M⊙. The X-rays from the extended intracluster medium thus reflect emission from the largest relaxed, self-gravitating entities known in the universe.

The issues one would like to understand both observationally and theoretically range from the internal and structural—What are the spatial gas density and temperature profiles? Intrinsic shapes? How do these relate to optical properties? How do they evolve with redshift?—to the global and statistical—What is the expected abundance of clusters as a function of luminosity, temperature or any other observable?