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.
The Integrated Sachs-Wolfe effect is a phenomenon in cosmology where the temperature of the cosmic microwave background (CMB) is affected by the gravitational potential of large-scale structures in the universe. It is a result of the interaction between photons from the CMB and the gravitational potential as they travel through the universe.
The Integrated Sachs-Wolfe effect provides valuable insight into the large-scale structure of the universe and the distribution of matter. It also helps to confirm the existence of dark energy, a mysterious force that is thought to be responsible for the accelerated expansion of the universe.
The Integrated Sachs-Wolfe effect is caused by the gravitational redshift and blueshift of photons as they travel through regions of varying gravitational potential. As photons pass through a region with a stronger gravitational pull, they lose energy (redshift) and as they pass through a region with a weaker gravitational pull, they gain energy (blueshift).
The Integrated Sachs-Wolfe effect is observed through measurements of the CMB temperature fluctuations. These fluctuations are mapped across the sky using telescopes and satellites, and any deviations from the expected temperature distribution can be attributed to the Integrated Sachs-Wolfe effect. Additionally, the effect can also be measured through the use of galaxy surveys which provide a map of the large-scale structure of the universe.
The Integrated Sachs-Wolfe effect has important implications for our understanding of the universe and its evolution. It provides evidence for the existence of dark energy and can also be used to study the growth of large-scale structures, such as galaxy clusters, in the universe. It also helps to constrain cosmological models and theories, leading to a better understanding of the overall structure and history of the universe.