Cosmological simulations of the intracluster medium

We investigate the properties of the intracluster medium (ICM) that forms within N-body/hydrodynamical simulations of galaxy clusters in a CDM cosmology. When radiative cooling and a simple model for galactic feedback are included, our clusters have X-ray luminosities and temperatures in good agreement with observed systems, demonstrating the required excess entropy in their cores. More generally, cooling and feedback increases the entropy of the ICM everywhere, albeit without significantly affecting the slope of the profile (S ∝ r ) at large radii. The temperature of the ICM is only modestly increased by these processes, with projected temperature profiles being in reasonable agreement with the observations. Star/galaxy formation is still too efficient in our simulations, however, and so our gas mass fractions are around 60 per cent of the observed value at r2500. Finally, we examine the reliability of using the hydrostatic equilibrium equation to estimate cluster masses and find that it underpredicts the true mass of our clusters by up to 20 per cent, due to incomplete thermalization of the gas. Feedback reduces this discrepancy, however, with estimates being accurate to within 10 per cent out to r500.