  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 1 Mpc 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 3 active plus 3
sterile neutrinos of equal mass, for which we deduce $1.51 \pm 0.04$ eV. The eV
mass range will be tested in the KATRIN experiment.
