X-RAY-EMISSION FROM A SIMULATED CLUSTER OF GALAXIES

Using the 1993 cluster simulation of Katz & White, we analyze the intr acluster medium and investigate the accuracy of the standard hydrostat ic method for determining cluster masses. We show that the simulated c luster gas is in hydrostatic equilibrium with a subsonic flow toward t he center. Inside a radius of approximately 100 kpc, this flow is in a steady state. The cooling time is shorter than a Hubble time within t he central 50 kpc. The flow rate is regulated by the gas sink in the m iddle of the cluster and the PdV work done as the gas flows in, verify ing the standard cooling flow scenario. We simulate observations of th e cluster using the instrument parameters of the EXOSAT ME detector an d the Einstein IPC detector. Even though the intracluster gas is not i sothermal, isothermal models of the cluster, excluding regions within 100 kpc of galaxies, fit the EXOSAT X-ray spectra as well as they fit real clusters. The X-ray surface brightness distribution is similar to that of real clusters, again excluding the galaxies. We simulate the procedure used to determine the masses of real clusters. We use the eq uation of hydrostatic equilibrium together with the temperature derive d from an isothermal fit to the simulated EXOSAT spectrum and the dens ity profile derived from a fit to the simulated IPC surface brightness profile to determine the mass. A comparison of the derived mass profi le to the actual mass profile shows that errors of a factor of 2 are p ossible. If the actual temperature profile is used, the cluster mass i s found to an accuracy of better than 25% within the virial radius.