A preference for a non-zero neutrino mass from cosmological data

Abstract

We present results from the analysis of cosmic microwave background (CMB), large-scale structure (galaxy redshift survey) and X-ray galaxy cluster (baryon fraction and X-ray luminosity function) data, assuming a geometrically flat cosmological model and allowing for tensor components and a non-negligible neutrino mass. From a combined analysis of all data, assuming three degenerate neutrino species, we measure a contribution of neutrinos to the energy density of the Universe, ωvh2 = 0.0059 -0.0027+0.0033 (68 per cent confidence limits), with zero falling on the 99 per cent confidence limit. This corresponds to ∼4 per cent of the total mass density of the Universe and implies a species-summed neutrino mass ∑i mi = 0.56-0.26+0.30 eV, or mv ∼ 0.2 eV per neutrino. We examine possible sources of systematic uncertainty in the results. Combining the CMB, large-scale structure and cluster baryon fraction data, we measure an amplitude of mass fluctuations on 8 h-1 Mpc scales of σ8 = 0.74-0.07+0.12, which is consistent with measurements based on the X-ray luminosity function and other studies of the number density and evolution of galaxy clusters. This value is lower than that obtained when fixing a negligible neutrino mass (σ8 = 0.86 -0.07+0.08). The combination of CMB, large-scale structure and cluster baryon fraction data also leads to remarkably tight constraints on the Hubble constant, H0 = 68.4-1.4+2.0 km s-1 Mpc-1, mean matter density, ωm = 0.31 ± 0.02, and physical baryon density, ωb h2 = 0.024 ± 0.001, of the Universe.