A uniform metal distribution in the intergalactic medium of the Perseus
  cluster of galaxies
  Most of the metals (elements heavier than helium) ever produced by stars in
the member galaxies of galaxy 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 of the cluster centers and enrichment with iron out to large
radii, leading to the idea that the metal enrichment occurred early in the
history of the Universe. Models with early enrichment predict a uniform metal
distribution at large radii in clusters, while late-time enrichment, favored by
some previous studies, is 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 measured iron
abundance, as a function of radius and azimuth, that is statistically
consistent with a constant value of 0.306+/-0.012 Solar 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, likely over 10 billion years ago, during the period of maximal star
formation and black hole activity.
