Cross correlation of the cosmic microwave background with radio sources: constraints on an accelerating universe.

We present a new limit on the cosmological constant based on the absence of correlations between the cosmic microwave background (CMB) and the distribution of distant radio sources. In cosmological constant, cold dark matter ( LambdaCDM) models, such correlations should have been produced via the integrated Sachs-Wolfe effect, assuming that radio sources trace the local ( z approximately 1) matter density. We find no evidence of correlations and obtain a 95% C.L. upper limit on the cosmological constant of Omega(Lambda)< or =0.74. If 0.6<Omega(Lambda)<0.7 as suggested by recent CMB anisotropy and supernovae observations, then the integrated Sachs-Wolfe effect should be detectable with upcoming CMB maps and radio surveys.