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 } \approx 0.27 and \Omega _ { \Lambda } \approx 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 \lesssim 2 ( ) .
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 ( ) 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 .