A SIMULATION OF THE INTRACLUSTER MEDIUM WITH FEEDBACK FROM CLUSTER GALAXIES

We detail method and report first results from a three-dimensional hyd rodynamical and N-body simulation of the formation and evolution of a Coma-sized cluster of galaxies, with the intent of studying the histor y of the hot, X-ray emitting intracluster medium. Cluster gas, galaxie s, and dark matter are included in the model. The galaxies and dark ma tter feel gravitational forces; the cluster gas also undergoes hydrody namical effects such as shock heating and PdV work. For the first time in three dimensions, we include modeling of ejection of processed gas from the simulated galaxies by winds, including heating and heavy ele ment enrichment. For comparison, we employ a ''pure infall'' simulatio n using the same initial conditions but with no galaxies or winds. We employ an extreme ejection history for galactic feedback in order to d efine the boundary of likely models. As expected, feedback raises the entropy of the intracluster gas, preventing it from collapsing to dens ities as high as those attained in the infall model. The effect is mor e pronounced in subclusters formed at high redshift. The cluster with feedback is always less X-ray luminous, but experiences more rapid lum inosity evolution, than the pure infall cluster. Even employing an ext reme ejection model, the final gas temperature is only similar to 15% larger than in the infall model. The radial temperature profile is ver y nearly isothermal within 1.5 Mpc. The cluster galaxies in the feedba ck model have a velocity dispersion similar to 15% lower than the dark matter. This results in the true ratio of specific energies in galaxi es to gas being less than one, beta(spec) similar to 0.7. The infall m odel predicts beta(spec), similar to 1.2. Large excursions in these va lues occur over time, following the complex dynamical history of the c luster. The morphology of the X-ray emission is little affected by fee dback. The emission profiles of both clusters are well described by th e standard beta-model with beta(fit) similar or equal to 0.7-0.9. X-ra y mass estimates based on the assumptions of hydrostatic equilibrium a nd the applicability of the beta-model are quite accurate in both case s. A strong, radial iron abundance gradient is present, which develops as a consequence of the steepening of the galaxy density profile over time. Spectroscopic observations using nonimaging detectors with wide (similar to 45') fields of view dramatically smear the gradient. Obse rvations with arcminute resolution, made available with the ASCA satel lite, would readily resolve the gradient.