The Integrated Sachs-Wolfe (ISW) effect supports the concept of dark energy through its correlation with Cosmic Microwave Background (CMB) anisotropies as observed in the NVSS-WMAP study. The research by Raccanelli et al. demonstrates that the NVSS radio sources' redshift distribution significantly impacts the cross-correlation with WMAP data, revealing that a bias factor decreasing with redshift aligns with Lambda-CDM cosmology predictions. This study confirms that the NVSS is more effective for ISW analysis than previously thought, reinforcing the evidence for dark energy and the accelerated expansion of the universe.
PREREQUISITESAstronomers, cosmologists, and astrophysicists interested in the relationship between dark energy and cosmic structure formation, as well as researchers analyzing CMB data and its implications for the universe's expansion.
We reassess the estimate of the cross-correlation of the spatial distribution of the NRAO VLA Sky Survey (NVSS) radio sources with that of Cosmic Microwave Background (CMB) anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP). This re-analysis is motivated by the fact that most previous studies adopted a redshift distribution of NVSS sources inconsistent with recent data. We find that the constraints on the bias-weighted redshift distribution, b(z)xN(z), of NVSS sources, set by the observed angular correlation function, w(theta), strongly mitigate the effect of the choice of N(z). If such constraints are met, even highly discrepant redshift distributions yield NVSS-WMAP cross-correlation functions consistent with each other within statistical errors. The models favoured by recent data imply a bias factor, b(z), decreasing with increasing z, rather than constant, as assumed by most previous analyses. As a consequence, the function b(z)xN(z) has more weight at z<1, i.e. in the redshift range yielding the maximum contribution to the ISW in a standard LambdaCDM cosmology. On the whole, the NVSS turns out to be better suited for ISW studies than generally believed, even in the absence of an observational determination of the redshift distribution. The NVSS-WMAP cross-correlation function is found to be fully consistent with the prediction of the standard LambdaCDM cosmology.