Most of the metals (elements heavier than helium) produced by stars in the member galaxies of clusters currently reside within the hot, X-ray-emitting intra-cluster gas. Observations of X-ray line emission from this intergalactic medium have suggested a relatively small cluster-to-cluster scatter outside the cluster centres1,2 and enrichment with iron out to large radii3,4,5, leading to the idea that the metal enrichment occurred early in the history of the Universe3. Models with early enrichment predict a uniform metal distribution at large radii in clusters, whereas those with late-time enrichment6,7 are expected to introduce significant spatial variations of the metallicity. To discriminate clearly between these competing models, it is essential to test for potential inhomogeneities by measuring the abundances out to large radii along multiple directions in clusters, which has not hitherto been done. Here we report a remarkably uniform iron abundance, as a function of radius and azimuth, that is statistically consistent with a constant value of ZFe = 0.306 ± 0.012 in solar units out to the edge of the nearby Perseus cluster. This homogeneous distribution requires that most of the metal enrichment of the intergalactic medium occurred before the cluster formed, probably more than ten billion years ago, during the period of maximal star formation and black hole activity.
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We are grateful for discussions with other members of the Perseus cluster Suzaku Key project collaboration, as well as with Y. Lu, P. Simeon and R. Blandford. This work was supported by the Suzaku grants NNX09AV64G and NNX10AR48G, the NASA ADAP grant NNX12AE05G, and by the US Department of Energy under contract number DE-AC02-76SF00515.
The authors declare no competing financial interests.
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Werner, N., Urban, O., Simionescu, A. et al. A uniform metal distribution in the intergalactic medium of the Perseus cluster of galaxies. Nature 502, 656–658 (2013). https://doi.org/10.1038/nature12646
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