New light on dark cosmos

Recent studies by a number of independent collaborations have correlated the cosmic microwave background temperatures measured by the Wilkinson Microwave Anisotropy Probe satellite with different galaxy surveys that trace the matter distribution with light from the whole range of the electromagnetic spectrum: radio, far-infrared, optical and X-ray surveys. The new data systematically find positive correlations, indicating a rapid slow down in the growth of structure in the Universe. Individual cross-correlation measurements are of low significance, but we show that combining data at different redshifts introduces important new constraints. Contrary to what happens at low redshifts, for a fixed Ωm, the higher the dark energy content, ΩΛ, the lower the integrated Sachs-Wolfe effect cross-correlation amplitude. At 68 per cent confidence level, the data find new independent evidence of dark energy: ΩΛ= 0.42–1.22. The data also confirm, to higher significance, the presence of a large dark matter component, Ωm= 0.18–0.34, exceeding the density of baryonic matter, but far from the critical value. Combining these new constraints with the prior of a flat universe, or the prior of an accelerating universe, provides strong new evidence for a dark cosmos. Combination with supernova data yields ΩΛ= 0.71 ± 0.13, Ωm= 0.29 ± 0.04. If we also assume a flat universe, we find ΩΛ= 0.70 ± 0.05 and w=−1.02 ± 0.17 for a constant dark energy equation of state.