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 the cosmological constant-cold dark matter ( \Lambda CDM ) models currently favored , such correlations should have been produced via the integrated Sachs-Wolfe effect , assuming that radio sources trace the local ( z \sim 1 ) matter density .
We find no evidence of correlations between the COBE 53Hz microwave map and the NVSS 1.4 GHz radio survey , and obtain an upper limit for the normalized cross-correlation of \langle \delta N \delta T \rangle / \sqrt { \langle \delta N ^ { 2 } \rangle \langle \delta T% ^ { 2 } \rangle } \leq 0.067 at the 95 % CL .
This corresponds to an upper limit on the cosmological constant of \Omega _ { \Lambda } \leq 0.74 , which is in marginal agreement with the values suggested by recent measurements of the CMB anisotropy and type-IA supernovae observations , \Omega _ { \Lambda } \simeq 0.6 - 0.7. If the cosmological model does lie in this range , then the integrated Sachs-Wolfe effect should be detectable with upcoming CMB maps and radio surveys .