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Recent work based on a global measurement of the ICM properties find evidencefor an increase of the iron abundance in galaxy clusters with temperaturearound 2-4 keV up to a value about 3 times larger than that typical of very hotclusters. We have started a study of the metal distribution in these objectsfrom the sample of Baumgartner et al. (2005), aiming at resolving spatially themetal content of the ICM. We report here on a 42ks XMM observation of the firstobject of the sample, the cluster Abell 2028. The XMM observation reveals acomplex structure of the cluster over scale of 300 kpc, showing an interactionbetween two sub-clusters in cometary-like configurations. At the leading edgesof the two substructures cold fronts have been detected. The core of the mainsubcluster is likely hosting a cool corona. We show that a one-component fitfor this region returns a biased high metallicity. This inverse iron bias isdue to the behavior of the fitting code in shaping the Fe-L complex. Inpresence of a multi-temperature structure of the ICM, the best-fit metallicityis artificially higher when the projected spectrum is modeled with a singletemperature component and it is not related to the presence of both Fe-L andFe-K emission lines in the spectrum. After accounting for the bias, the overallabundance of the cluster is consistent with the one typical of hotter, moremassive clusters. We caution the interpretation of high abundances inferredwhen fitting a single thermal component to spectra derived from relativelylarge apertures in 3-4 keV clusters, because the inverse iron bias can bepresent. Most of the inferences trying to relate high abundances in 3-4 keVclusters to fundamental physical processes will likely have to be revised.

Apparent high metallicity in 3-4 keV galaxy clusters: the inverse iron-bias in action in the case of the merging cluster Abell 2028