THE DISTRIBUTION OF IRON IN THE PERSEUS CLUSTER

THE hot (∼108 K) gas that permeates clusters of galaxies may be primordial matter left over from the initial density perturbation that grew into the cluster, or may be gas ejected from cluster galaxies. The detection of iron emission features in cluster X-ray spectra proves that at least some of the intracluster medium (ICM) is not primordial, and much theoretical modelling of clusters has been based on the assumption that the entire ICM derives from the galaxies. We report here hard-X-ray spectral imaging observations of the Perseus cluster obtained with the coded-mask X-ray telescope on Spacelab 2 which reveal an iron abundance gradient in the ICM. Most of the ICM seems to be primordial, with the iron-rich gas confined largely to the cluster core where it was probably deposited by stripping of cluster galaxies. The total mass of iron required to explain the X-ray spectra is substantially smaller than has been assumed on the basis of a chemically homogeneous ICM. © 1990 Nature Publishing Group.