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

In this paper, we investigate the effect of cooling on the X-ray properties of galaxy clusters. We have performed N-body, hydrodynamical simulations b oth with and without the effects of radiative cooling, but neglecting the e ffects of star formation and feedback. We show that radiative cooling produ ces an inflow of high-entropy gas from the outer parts of the cluster, thus raising the cluster temperature and decreasing the X-ray luminosity. With radiative cooling clusters are on average from three to five times less lum inous in X-rays than the same clusters simulated without cooling. However, we do not produce a large constant-density core in either the gas or the da rk matter distributions. Our results contradict previous work in which cool ing raises the X-ray luminosity and deposits an unreasonably large amount o f mass in the central cluster galaxy. We achieve this by selecting our nume rical resolution in such a way that a reasonable fraction of the baryonic m aterial cools and by decoupling the hot and cold gas in our simulations, a first step towards modelling multiphase gas. We emphasize that globally coo ling a sensible amount of material is vital and the presence or absence of massive central concentrations of cold baryonic material has a dramatic eff ect upon the resultant X-ray properties of the clusters.