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 .