The discussion centers on the Integrated Sachs-Wolfe (ISW) effect and its implications for dark energy, particularly in relation to the Lambda-CDM cosmology. Participants explore the correlation between NVSS radio sources and CMB anisotropies from WMAP, examining how this relates to the understanding of dark energy and the accelerated expansion of the universe.
Participants express varying levels of understanding and seek clarification on specific aspects of the ISW effect and its implications for dark energy. There is no consensus reached on the interpretation of the findings or their implications.
The discussion highlights potential limitations in the assumptions regarding redshift distributions and their impact on the analysis of the ISW effect. The dependence on statistical errors in the correlation functions is also noted.
This discussion may be of interest to those studying cosmology, dark energy, and the methodologies used in analyzing cosmic microwave background data.
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.