  The lensing data of the galaxy cluster Abell 1689 can be explained by an
isothermal fermion model with a mass of 1-2 eV. The best candidate is the 1.5
eV neutrino; its mass will be searched down to 0.2 eV in KATRIN 2015. If its
righthanded (sterile) modes were created too, there is 20% neutrino hot dark
matter. Their condensation on clusters explains the reionization of the
intercluster gas without Pop. III stars. Baryonic structure formation is
achieved by gravitional hydrodynamics alone, without dark matter trigger.
