The extended ROSAT-ESO Flux-Limited X-ray Galaxy Cluster Survey (REFLEX II) VI. Effect of massive neutrinos on the cosmological constraints from clusters

Clusters of galaxies are important probes for the large-scale structure that allow us to test cosmological models. With the REFLEX II galaxy cluster survey we previously derived tight constraints on the cosmological parameters for the matter density, Omega(m), and the amplitude parameter of the matter density fluctuations, sigma(8). Whereas in these previous studies no effect of massive neutrinos was taken into account, we explore these effects in the present publication. We derive cosmological constraints for the sum of the neutrino masses of the conventional three neutrino families in the range M-v = Sigma(i) m(v) i = 0 to 0.6 eV. The influence on the constraints of Omega(m) and sigma(s) for the expected mass range is weak. Interesting constraints on the neutrino properties can be derived by comparing the cluster data with those from the Planck cosmic microwave background observations. The current tension between the Planck results and clusters can formally be resolved with neutrino masses of about M-v = 0.45(+/- 0.28, 1 sigma) eV. While we caution not to consider this a firm measurement because it might also be the result of unresolved systematics, it is interesting that other measurements of the local large-scale structure fluctuation amplitude, like that of cosmic lensing shear, yield similar results and additionally confirm the effect of massive neutrinos. Among the indicators for massive neutrinos, galaxy clusters and in particular our large and well-controlled cluster survey currently provide the best potential for constraints of the total neutrino mass.