The distribution of dark matter in the Perseus cluster

Abstract

We report on the analysis of spatially resolved spectral images of the Perseus cluster obtained with a coded-mask X-ray telescope flown as part of the Spacelab 2 mission. The data allow the temperature and density profiles of the intracluster gas to be measured. From these the cluster potential and hence the cluster mass as a function of radius can be traced. The results show that there is significantly less dark matter in the cluster than implied by virial mass estimates based on the galaxies. The mass-to-light ratio within 1.3h_50_ Mpc of the cluster center is found to be ~100(M_sun_/L_sun_). The dark matter is more centrally condensed than the X-ray-emitting gas and probably more so than the galaxies, contrary to expectations from most cosmogonic scenarios. We show that the conclusions are rather robust and insensitive to different parameterizations and assumptions about the X-ray structure and argue that they favor models in which the dark matter is baryonic.