First YearWilkinson Microwave Anisotropy ProbeObservations: Dark Energy Induced Correlation with Radio Sources

The first-year WMAP data, in combination with any one of a number of othercosmic probes, show that we live in a flat \Lambda-dominated CDM universe with\Omega_m ~ 0.27 and \Omega_\Lambda ~ 0.73. In this model the late-time actionof the dark energy, through the integrated Sachs-Wolfe effect, should produceCMB anisotropies correlated with matter density fluctuations at z<2 (Crittenden& Turok 1996). The measurement of such a signal is an important independentcheck of the model. We cross-correlate the NRAO VLA Sky Survey radio sourcecatalog (Condon et al. 1998) with the WMAP data in search of this signal, andsee indications of the expected correlation. Assuming a flat \Lambda-CDMcosmology, we find \Omega_\Lambda>0 (95% CL, statistical errors only) with thepeak of the likelihood at \Omega_\Lambda=0.68, consistent with the preferredWMAP value. A closed model with \Omega_m=1.28, h=0.33, and no dark energycomponent (\Omega_\Lambda=0), marginally consistent with the WMAP CMB TTangular power spectrum, would produce an anti-correlation between the matterdistribution and the CMB. Our analysis of the cross-correlation of the WMAPdata with the NVSS catalog rejects this cosmology at the 3\sigma level.Comment: 13 pages, 4 figures, submitted to Ap