2013MNRAS.434.2679N

Recent weak and strong lensing data of the galaxy cluster A1689 are modelled by dark fermions that are quantum degenerate within some core. The gas density, deduced from X-ray observations up to 1Mpc and obeying a cored power law, is taken as input, while the galaxy mass density is modelled. An additional dark matter tail may arise from cold or warm dark matter, axions or non-degenerate neutrinos. The fit yields that the fermions are degenerate within a 430-kpc radius. The fermion mass is a few eV and the best case involves three active plus three sterile neutrinos of equal mass, for which we deduce 1.51±0.04 eV. The eV mass range will be tested in the KATRIN experiment.