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Abstract: The cluster baryon fraction is estimated from the CMB-scattering leptoniccomponent of the intracluster medium ICM; however, the observed clusterbaryon fraction is less than the cosmic one. Understanding the origin of thisdiscrepancy is necessary for correctly describing the structure of the ICM. Weestimate the baryonic mass in the outskirts of galaxy clusters which isdifficult to observe because of low electron temperature and density in theseregions. The time scale for the electrons and protons to reach equipartition inthe outskirts is longer than the cluster age. Since thermal equilibrium is notachieved, a significant fraction of the ICM baryons may be hidden in shellsaround galaxy clusters. We derive the necessary condition on the cluster massfor the concealment of missing baryons in an outer baryon shell and show thatthis condition is fulfilled because cluster masses are comparable to theestimated characteristic mass $M=e^4-m^3 {p} G^2=1.3x10^{15}$ solar masses.The existence of extreme-ultraviolet emission haloes around galaxy clusters ispredicted.



Author: Dmitry Prokhorov

Source: https://arxiv.org/



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