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Magnetic Fields in Cooling Flow Clusters: A Critical View

Shortly after the first results of Chandra and XMM-Newton appeared, many researchers in the field abandoned the term "cooling flow clusters" in favor of the name "cool core clusters". This change, I argue, has been causing damage by promoting the view that there is no substantial cooling in these clusters. In this contribution I discuss the following points, with emphasize on the last one that deals with magnetic fields in cooling flow clusters. (1) Both AGN-feedback and hot-gas cooling to form stars occur during galaxy formation as well as in cooling flow clusters. Ignoring cooling of the intra-cluster medium, as implied by the term "cool core", does not encourage comparative study of AGN feedback in cooling flow clusters with that of galaxy formation. (2) The line of thought that there is no cooling might lead to wrong questions and research directions. (3) A key question in both cooling flow clusters and during galaxy formation is the mode of accretion by the super massive black hole (SMBH). When cooling is neglected only accretion from the hot phase remains. Accretion from the hot phase, such as the Bondi accretion, suffers from some severe problems. (4) When it is accepted that moderate quantities of gas are cooling, it becomes clear that global heat conduction must be substantially suppressed. This does not favor a globally ordered magnetic field. As well, it makes global heat conduction unattractive.