Combined analysis of the integrated Sachs-Wolfe effect and cosmological implications

TL;DR

This work performs a global ISW measurement by cross-correlating multiple galaxy surveys (2MASS, SDSS galaxies, SDSS MegaZ LRGs, NVSS, HEAO, SDSS QSO) with WMAP CMB data, carefully modeling covariances across surveys. The ISW signal is detected at ≈4.5σ, and the analysis shows consistency with flat ΛCDM (Ωm ≈ 0.2–0.26, w ≈ -1) when combined with BAO and SNe data, with no strong evidence for evolving dark energy or nonstandard sound speeds. The study emphasizes a covariance-aware, joint approach to ISW analyses, demonstrates frequency- and mask-robust results, and provides detailed covariance matrices and methodological comparisons across error estimators. Overall, the results reinforce the concordance ΛCDM model and illustrate the ISW effect as a robust probe of dark energy and cosmic curvature.

Abstract

We present a global measurement of the integrated Sachs-Wolfe (ISW) effect obtained by cross-correlating all relevant large scale galaxy data sets with the cosmic microwave background radiation map provided by the Wilkinson Microwave Anisotropy Probe. With these measurements, the overall ISW signal is detected at the ~ 4.5 sigma level. We also examine the cosmological implications of these measurements, particularly the dark energy equation of state w, its sound speed, and the overall curvature of the Universe. The flat LCDM model is a good fit to the data and, assuming this model, we find that the ISW data constrain Omega_m = 0.20 +0.19 -0.11 at the 95% confidence level. When we combine our ISW results with the latest baryon oscillation and supernovae measurements, we find that the result is still consistent with a flat LCDM model with w = -1 out to redshifts z > 1.

Figures (15)

• Figure 1: The redshift distributions of all catalogues $dN/dz$ normalised to unity. The significant overlap between redshift distributions (especially for the X-ray and radio surveys) results in a covariance matrix with significant non-diagonal elements.
• Figure 2: Measures of the two-point correlation functions between all the combinations of catalogues, where the units in the x-axis are degrees. The auto-correlations are on the diagonal, and the solid (red) lines show the theory from WMAP best fit cosmology and the galactic bias from the literature. The largest discrepancy with theory, in the NVSS-2MASS CCF, can be addressed by a small change in the assumed NVSS redshift distribution (blue dashed line).
• Figure 3: Monte Carlo error estimation. Measurements of the cross-correlation functions between all the catalogues and the WMAP CMB maps (black points), compared with the theory from WMAP best fit cosmology and the galactic bias from the literature (red solid lines). The best fit amplitudes and their $1-\sigma$ deviations are shown in blue (dashed). In the top panel, the errors are calculated with 5000 temperature-only Monte Carlos and, in the bottom panel, Monte Carlos for temperature and density including expected correlations. We see that the errors are comparable for individual observations. Because of known contamination from the Sunyaev-Zeldovich effect in the 2MASS data Afshordi:2003xu, the four smallest angle bins were excluded from the fits.
• Figure 4: Jack-knife error estimation. The lines are the same as in Fig. \ref{['fig:ccf-all']}. The errors are somewhat smaller than seen from the Monte Carlo estimates, possibly due to correlations between the jack-knife subsamples.
• Figure 5: The total covariance matrix obtained with 5000 Monte Carlos, normalised. The top panel shows the temperature-only Monte Carlos, while the bottom panel is the result of the full Monte Carlos. While the diagonal (single experiment) covariances are similar, those between experiments (off-diagonal) are somewhat different.