Observations in the UV and optical indicate that star formation rates in clusters are only a small fraction of those predicted by the cooling flow model (see e.g. In addition, cooling flows are expected to deposit cool gas in the centres of groups and clusters, so we would expect to see large amounts of molecular gas and high star formation rates towards cluster centres. First of all, observations of the Fe L-line complex, which is a precise tool for measuring the amount of gas cooling at low temperatures, have revealed a much smaller amount of cooling gas with a temperature 2–3 times smaller than the virial temperature, than is predicted by the cooling flow model (McNamara &įabian, 2006). However, this simple cooling flow model has trouble explaining the observed properties of groups and clusters. Assuming that there are no heating processes at play in the core of these clusters, we would expect radiative cooling to result in a cooling flow, with a deposition rate of a few 100 M ⊙ yr − 1 (for a review, see Fabian, 1994). For about 50% of clusters, the core cooling time is shorter than the age of the cluster itself (e.g. Cooling flows are one of these processes. The deviation of the observed scaling relations for clusters from self-similarity, implies the existence of processes which act to heat and cool the ICM. our entropy profiles do not flatten out at small radii, as suggested by some previous studies. We do not find evidence for the existence of an “entropy floor”, i.e. We find that the entropy profiles are well-fitted by a simple powerlaw model, of the form K ( r ) = α × ( r / 100 k p c ) β, where α and β are constants. Entropy profiles can therefore be used to examine any deviations from cluster self-similarity, as well as the effects of 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.
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. 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.
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