A volume-limited sample of X-ray galaxy groups and clusters - I. Radial entropy and cooling time profiles

We present the first results of our study of a sample of 101 X-ray galaxy groups and clusters, which is volume-limited in each of three X-ray luminosity bins. The aim of this work is to study the properties of the innermost ICM in the cores of our groups and clusters, and to determine the effect of non-gravitational processes, such as active galactic nucleus (AGN) feedback, on the ICM. The entropy of the ICM is of special interest, as it bears the imprint of the thermal history of a cluster, and it also determines a cluster's global properties. Entropy profiles can therefore be used to examine any deviations from cluster self-similarity, as well as the effects of feedback on the ICM. We find that the entropy profiles are well-fitted by a simple power-law model, of the form K(r) = alpha x (r/100 kpc)(beta), where alpha and beta are constants. We do not find evidence for the existence of an 'entropy floor', i.e. our entropy profiles do not flatten out at small radii, as suggested by some previous studies.