First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Dark Energy Induced Correlation with Radio Sources
The first-year WMAP data, in combination with any one of a number of other cosmic 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 action of the dark energy, through the integrated Sachs-Wolfe effect, should produce CMB anisotropies correlated with matter density fluctuations at z<2 (Crittenden & Turok 1996). The measurement of such a signal is an important independent check of the model. We cross-correlate the NRAO VLA Sky Survey radio source catalog (Condon et al. 1998) with the WMAP data in search of this signal, and see indications of the expected correlation. Assuming a flat \Lambda-CDM cosmology, we find \Omega_\Lambda>0 (95% CL, statistical errors only) with the peak of the likelihood at \Omega_\Lambda=0.68, consistent with the preferred WMAP value. A closed model with \Omega_m=1.28, h=0.33, and no dark energy component (\Omega_\Lambda=0), marginally consistent with the WMAP CMB TT angular power spectrum, would produce an anti-correlation between the matter distribution and the CMB. Our analysis of the cross-correlation of the WMAP data with the NVSS catalog rejects this cosmology at the 3\sigma level.