Measurement of the gravitational potential evolution from the cross-correlation betweenWMAPand the APM Galaxy Survey

Models with late-time cosmic acceleration, such as the Λ-dominated cold dark matter model, predict a freeze-out for the growth of linear gravitational potential at moderate redshift z < 1, which can be observed as temperature anisotropies in the cosmic microwave background (CMB): the so-called integrated Sachs–Wolfe (ISW) effect. We present a direct measurement of the ISW effect based on the angular cross-correlation function, wTG(θ), of CMB temperature anisotropies and dark matter fluctuations traced by galaxies. We cross-correlate the first-year WMAP data in combination with the APM Galaxy Survey. On the largest scales, θ= 4°–10°, we detect a non-vanishing cross-correlation at 98.8 per cent significance level, with a 1σ error of wTG= 0.35 ± 0.14 μK, which favours large values of ΩΛ≃ 0.8 for flat Friedmann–Robertson–Walker models. On smaller scales, θ < 1°, the correlations disappear. This is contrary to what would be expected from the ISW effect, but the absence of correlations may be simply explained if the ISW signal was being cancelled by anti-correlations arising from the thermal Sunyaev–Zeldovich effect.