Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Measurement of the gravitational potential evolution from the cross-correlation between WMAP and the APM Galaxy survey

Pablo Fosalba, Enrique Gaztanaga

TL;DR

This work reports a direct detection of the ISW effect by cross-correlating the CMB temperature from WMAP with the APM galaxy survey, finding a positive cross-correlation on angular scales $\theta\sim4$–$10°$ that supports evolving gravitational potentials in a ΛCDM universe. The measured $w_{TG}(\theta)$, $0.35\pm0.13\ \mu$K, agrees with ISW predictions for $\Omega_\Lambda\approx0.8$, while the lack of signal on smaller scales is consistent with a SZ-induced anti-correlation $w_{TG}^{SZ}\approx -0.41\ \mu$K, allowing bounds on cluster-related parameters. The analysis uses robust error estimation via jackknife and Monte Carlo simulations and highlights the impact of secondary anisotropies on small scales. Overall, the results reinforce ΛCDM with a significant late-time evolution of gravitational potentials and illustrate how SZ contaminates the ISW signal at small scales.

Abstract

Models with late time cosmic acceleration, such as the Lambda-dominated CDM model, predict a freeze out for the growth of linear gravitational potential at moderate redshift z<1, what can be observed as temperature anisotropies in the CMB: the so called integrated Sachs-Wolfe (ISW) effect. We present a direct measurement of the ISW effect based on the angular cross-correlation function, w_{TG}, of CMB temperature anisotropies and dark-matter fluctuations traced by galaxies. We cross-correlate the first-year WMAP data in combination with the APM Galaxy survey. On the largest scales, theta = 4-10 deg, we detect a non-vanishing cross-correlation at 98.8 % significance level, with a 1-sigma error of w_{TG} = 0.35 +/- 0.14 microK, which favors large values of Omega_Lambda \simeq 0.8 for flat FRW models. On smaller scales, theta < 1deg, the correlations disappear. This is contrary to what would be expected from the ISW effect, but the absence of correlations may be simply explained if the ISW signal was being cancelled by anti-correlations arising from the thermal Sunyaev-Zeldovich (SZ) effect.

Measurement of the gravitational potential evolution from the cross-correlation between WMAP and the APM Galaxy survey

TL;DR

This work reports a direct detection of the ISW effect by cross-correlating the CMB temperature from WMAP with the APM galaxy survey, finding a positive cross-correlation on angular scales – that supports evolving gravitational potentials in a ΛCDM universe. The measured , K, agrees with ISW predictions for , while the lack of signal on smaller scales is consistent with a SZ-induced anti-correlation K, allowing bounds on cluster-related parameters. The analysis uses robust error estimation via jackknife and Monte Carlo simulations and highlights the impact of secondary anisotropies on small scales. Overall, the results reinforce ΛCDM with a significant late-time evolution of gravitational potentials and illustrate how SZ contaminates the ISW signal at small scales.

Abstract

Models with late time cosmic acceleration, such as the Lambda-dominated CDM model, predict a freeze out for the growth of linear gravitational potential at moderate redshift z<1, what can be observed as temperature anisotropies in the CMB: the so called integrated Sachs-Wolfe (ISW) effect. We present a direct measurement of the ISW effect based on the angular cross-correlation function, w_{TG}, of CMB temperature anisotropies and dark-matter fluctuations traced by galaxies. We cross-correlate the first-year WMAP data in combination with the APM Galaxy survey. On the largest scales, theta = 4-10 deg, we detect a non-vanishing cross-correlation at 98.8 % significance level, with a 1-sigma error of w_{TG} = 0.35 +/- 0.14 microK, which favors large values of Omega_Lambda \simeq 0.8 for flat FRW models. On smaller scales, theta < 1deg, the correlations disappear. This is contrary to what would be expected from the ISW effect, but the absence of correlations may be simply explained if the ISW signal was being cancelled by anti-correlations arising from the thermal Sunyaev-Zeldovich (SZ) effect.

Paper Structure

This paper contains 5 sections, 4 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Data & simulations
  3. WMAP-APM Cross-Correlation
  4. Comparison with Predictions
  5. Discussion

Figures (3)

  • Figure 1: APM galaxy density fluctuation maps (top panels) compared to WMAP (V-band) maps (bottom panels) and the cross-correlation map (middle). In each case left panels show the maps smoothed with a Gaussian beam of FWHM $=5$ deg, while right panels have FWHM $=0.7$ deg. We use normalized units (dimensionless) with linear color scheme in the range ($-3\sigma,+3\sigma$), being $\sigma$ the pixel variance in each map.
  • Figure 2: Comparing measurement to predictions: The two solid lines and the dotted line show $w_{TG}$ results for WMAP bands V, W, and the foreground "cleaned" map. Boxes give the $68\%$ confidence levels. Also shown are the theoretical predictions for ISW and SZ (upper and lower short-dashed lines) and their sum (long-dashed line) for the best-fit model with $\Omega_{\Lambda}\simeq 0.8$.
  • Figure 3: Errors in the cross-correlation $w_{TG}(\theta)$ from the dispersion in 200 Monte-Carlo simulations (solid line) as compared with the mean and dispersion (squares with errobars) in the jack-knife error estimation over the same simulations. Dashed line correspond to the jack-knife error in the real WMAP-APM sample.