Galaxy feedback and cluster evolution.

Abstract

We detail method and report results from an ensemble of three-dimensional hydrodynamical and N-body simulations of the formation and evolution of clusters of galaxies, with the primary intent of studying the history of the hot, X-ray emitting intracluster medium. Cluster gas, galaxies, and dark matter are included in the model. The galaxies and dark matter feel gravitational forces; the cluster gas also undergoes hydrodynamical effects such as shock heating and PdV work. For the first time in three dimensions, we include modelling of ejection of processed gas from the simulated galaxies by winds, including heating and heavy element enrichment. For comparison, we employ 'pure infall' simulations using the same initial conditions but with no galaxies or winds. We employ an extreme ejection history for galactic feedback in order to define the boundary of likely models. Heating from winds raises the entropy of the intracluster gas, resulting in a more extended gas distribution for the ejection ensemble than for the simple, two-fluid runs. Winds thus diminish cluster X-ray luminosities, but result in more rapid luminosity evolution. A density gradient with respect to cluster galaxies causes an abundance gradient; the strength of the gradient is sensitive to the particular wind model assumed. An empirical model for the dark matter distribution, combined with an assumption of hydrostatic equilibrium, can reproduce many cluster properties, but predictions at small radii cannot be tested due to numerical resolution limits. Cluster galaxy velocities are biased compared to the dark matter; this velocity bias, combined with wind heating, causes a relation between velocity dispersion and temperature steeper than expected theoretically and consistent with observations. When compared with observations, the simulated clusters with winds are underluminous for a given temperature. Luminosity functions constructed from the luminosity-mass correlation for each ensemble bracket the observational data. The results suggest a less extreme wind model, in a low-density universe with a baryon fraction of $\sim$20%, could reproduce many observed properties of X-ray clusters as well as the cluster X-ray luminosity function.