Heating the intergalactic medium by radiative decay of neutrinos
  Assuming that there exists a species of heavy sterile neutrinos($m_{\nu}>1$ keV) and their decays can serve as a heating source of the hot gas in galaxy clusters, we study how the observational constraints on cooling flow limit the mass of these sterile neutrinos. We predict a relation among the luminosity, total mass and the redshift of a cluster, and we compare this relation with data from 12 clusters to obtain an estimate of the decay rate of the sterile neutrino. 
M. H. Chan and M.-C. Chu