Is the Gas in Cooling Flows Multiphase?

Abstract

Employing XMM-Newton EPIC data we perform a detailed comparison between different spectral models to test whether the gas in cooling flows is multiphase or not. Our findings all point in the same direction, namely, that gas in cooling flows does not show the wide distribution of temperatures expected from standard multiphase models. This result has profound implications for cooling-flow models. First, the large absorption column depths inferred by previous analysis of cooling-flow spectra are most likely an artifact following from the application of an incorrect spectral model to the data. Second, the mass deposition and mass flow are likely to be much smaller than previously thought. Last, but perhaps not least, the term "cooling-flow" cluster is probably no longer appropriate, as it describes a phenomenon of smaller entity and impact than previously thought. We propose to substitute it with that of "cool-core" cluster. The latter definition is less ambitious than the first, as it reflects only an observational fact rather than an inferred physical property, the flow, but has the undeniable advantage of being firmer.