Measurement of the gravitational potential evolution from the cross-correlation between WMAP and the APM Galaxy survey

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Abstract
Cosmological models with late time cosmic acceleration, such as the Lambda-dominated FRW model, predict a freeze out for the gravitational growth of large scale (linear) dark-matter fluctuations at moderate redshift z<1. This leaves an imprint on the dynamics of the gravitational potential that can be observed as temperature fluctuations in the 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, w_TG(theta)=, of CMB temperature anisotropies Delta_T, and dark-matter fluctuations traced by galaxies delta_G. We use the best current data to trace such anisotropies: the first-year WMAP data in combination with the APM Galaxy survey. On the largest scales, theta = 5-10 deg, our analysis yields w_TG = 0.35 +/- 0.20 uK (90% C.L.), what favors large values of Omega_Lambda = 0.3-0.8 for flat FRW models. The measured cross-correlation is slightly larger than, but in good agreement with, recent analysis based on X-ray and radio sources (Boughn & Crittenden 2003, Nolta etal. 2003). On smaller scales, theta < 1 deg, one expects a comparable ISW contribution. Instead we find a negative correlation w_{TG} = -0.2 +/- 0.2 uK. Although such scales are dominated by sampling variance, our analysis clearly indicates a cancellation of ISW with inverse Compton scattering in the hot gas in galaxy clusters, ie the thermal Sunyaev-Zeldovich (SZ) effect. The SZ contribution is w_TG = -0.5 +/- 0.2 +/- 0.2 uK (90% C.L.), which can be used to set new limits on the total mean Compton distortion of CMB photons.

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