The effect of radiative cooling on the X-ray properties of galaxy clusters

Abstract

In this paper, we investigate the effect of cooling on the X-ray properties of galaxy clusters. We have performed N-body, hydrodynamical simulations both with and without the effects of radiative cooling, but neglecting the effects of star formation and feedback. We show that radiative cooling produces an inflow of high-entropy gas from the outer parts of the cluster, thus \emph{raising} the cluster temperature and \emph{decreasing} the X-ray luminosity. With radiative cooling clusters are on average three to five times less luminous in X-rays than the same cluster simulated without cooling. However, we do not produce a large constant-density core in either the gas or the dark matter distributions. Our results contradict previous work in which cooling raises the X-ray luminosity and deposits an unreasonably large amount of mass in the central cluster galaxy. We achieve this by selecting our numerical resolution in such a way that a reasonable fraction of the baryonic material cools and by decoupling the hot and cold gas in our simulations, a first step towards modelling multiphase gas. We emphasise that globally cooling a sensible amount of material is vital and the presence or absence of massive central concentrations of cold baryonic material has a dramatic effect upon the resultant X-ray properties of the clusters.