How Does the Integrated Sachs-Wolfe Effect Support the Concept of Dark Energy?

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The Integrated Sachs-Wolfe (ISW) effect provides evidence for dark energy by demonstrating how gravitational potential wells evolve over time in an expanding universe. The recent study reassesses the correlation between NVSS radio sources and Cosmic Microwave Background (CMB) anisotropies from WMAP, revealing that the NVSS data aligns with Lambda-CDM cosmology predictions. The findings indicate that the bias-weighted redshift distribution of NVSS sources significantly influences the observed correlations, particularly favoring models where the bias decreases with redshift. This suggests that the NVSS is more effective for ISW studies than previously thought, supporting the notion of accelerated cosmic expansion due to dark energy. Ultimately, the consistent NVSS-WMAP cross-correlation reinforces the understanding of dark energy's role in the universe's expansion.
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Can someone please translate for me what is really meant when saying that,

"The NVSS–WMAP CCF is found to be fully consistent with the prediction of the standard Lambda-CDM cosmology."
 
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Reference?

Garth
 
A reassessment of the evidence of the Integrated Sachs–Wolfe effect
through the WMAP–NVSS correlation
A. Raccanelli,1 A. Bonaldi,1,2 M. Negrello,3 S. Matarrese,4 G. Tormen1
and G. De Zotti2,5
 
A reassessment of the evidence of the Integrated Sachs-Wolfe effect through the WMAP-NVSS correlation
Abstract
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.
 
Can you tell me how the ISW supports dark energy, i.e. the accelerated expansion?
 
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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