The case of 1.5 eV neutrino hot dark matter

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.