In the context of the study of the integrated Sachs Wolfe effect (ISW), werevisit the angular cross correlation of WMAP cosmic microwave background(CMB) data with the NRAO Very Large Array Sky Survey (NVSS). We compute2-point cross functions between the two surveys, both in real and in Fourierspace, paying particular attention on the dependence of results on the flux ofNVSS radio sources, the angular scales where correlations arise and thecomparison with theoretical expectations. We reproduce previous results thatclaim an excess of correlation in the angular correlation function (ACF), andwe also find some (low significance, 2-)similarity betweenthe CMB and radio galaxy data in the multipole range .However,the signal to noise ratio (S/N) in the ACFs increases with higher fluxthresholds for NVSS sources, but drops a in separations of theorder of a pixel size, suggesting some residual point sourcecontribution. When restricting our analyses to multipoles l<60, we fail tofind any evidence for cross correlation in the range ,whereaccording to the model predictions and our simulations 50% of the S/Nis supposed to arise. Also, the accumulated S/N for l<60 is below 1, farfrom the theoretical expectation of .Part of this disagreementmay be caused by an inaccurate modeling of the NVSS source population: as inprevious works, we find a level of large scale (l<70) clustering in the NVSScatalog that seems incompatible with a high redshift population. This largescale clustering excess is unlikely to be caused by contaminants orsystematics, since it is independent of flux threshold, and hence present forthe brightest, most clearly detected (>)NVSS sources. Either ourNVSS catalogs are not probing the high redshift, large scale gravitationalpotential wells, or there is a clear mismatch between the ISW componentpresent in WMAP data and theoretical expectations.Key words: cosmic microwave background - large scale structure of Universe
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