The Effect of Cooling and Preheating on the X-ray Properties of Clusters of Galaxies

We calculate X-ray properties of present-day galaxy clusters from hydrodynamical cosmological simulations of the LCDM cosmology and compare these with recent X-ray observations. Results from three simulations are presented, each of which uses the same initial conditions: a standard adiabatic, Non-radiative model, a Radiative model that includes radiative cooling of the gas, and a Preheating model that also includes cooling but in addition impulsively heats the gas prior to cluster formation. At the end of the simulations, the global cooled baryon fractions in the latter two runs are 15 per cent and 0.4 per cent respectively which bracket the recent result from the K-band luminosity function. We construct cluster catalogues which consist of over 500 clusters and are complete in mass down to 1.18*10^{13} Msun/h. While clusters in the Non-radiative model behave in accord with the self-similar picture, those of the other two models reproduce key aspects of the observed X-ray properties: the core entropy, temperature-mass and luminosity-temperature relations are all in good agreement with recent observations. This agreement stems primarily from an increase in entropy with respect to the Non-radiative clusters. Although the physics affecting the intra-cluster medium is very different in the two models, the resulting cluster entropy profiles are very similar.