A uniform metallicity in the outskirts of massive, nearby galaxy clusters

Suzaku measurements of a homogeneous metal distribution of Z ∼ 0.3 Solar in the outskirts of the nearby Perseus cluster suggest that chemical elements were deposited and mixed into the intergalactic medium before clusters formed, likely over 10 billion years ago. A key prediction of this early enrichment scenario is that the intracluster medium in all massive clusters should be uniformly enriched to a similar level. Here, we confirm this prediction by determining the iron abundances in the outskirts (r > 0.25r₂₀₀) of a sample of 10 other nearby galaxy clusters observed with Suzaku for which robust measurements based on the Fe-K lines can be made. Across our sample, the iron abundances are consistent with a constant value, Z_Fe = 0.316 ± 0.012 Solar (χ² = 28.85 for 25 degrees of freedom). This is remarkably similar to the measurements for the Perseus cluster of Z_Fe = 0.314 ± 0.012 Solar, using the Solar abundance scale of Asplund et al.