Do non-relativistic neutrinos constitute the dark matter?

Abstract

The dark matter of the Abell 1689 Galaxy Cluster is modeled by thermal, non-relativistic gravitating fermions and its galaxies and X-ray gas by isothermal distributions. A fit yields a mass of h701/2(12/g)1/4 1.445(30) eV. A dark-matter fraction Ων=h70-3/20.1893(39) occurs for = 12 degrees of freedom, i.e., for 3 families of left- plus right-handed neutrinos with masses ≈23/4GF1/2me2. Given a temperature of 0.045 K and a de Broglie length of 0.20 mm, they establish a quantum structure of several million light years across, the largest known in the Universe. The virial α-particle temperature of 9.9±1.1 keV/kB coincides with the average one of X-rays. The results are compatible with neutrino genesis, nucleosynthesis and free streaming. The neutrinos condense on the cluster at redshift z∼28, thereby causing reionization of the intracluster gas without assistance of heavy stars. The baryons are poor tracers of the dark-matter density. © EPLA, 2009.