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Cross-correlation of WMAP 3rd year and the SDSS DR4 galaxy survey: new evidence for Dark Energy

A. Cabre, E. Gaztanaga, M. Manera, P. Fosalba, F. Castander

TL;DR

The paper tests the late ISW effect as evidence for dark energy by cross-correlating WMAP3 CMB temperature data with SDSS DR4 galaxy maps over ~13% of the sky. Using two galaxy subsamples and robust covariance analyses, the authors detect a significant cross-correlation with $S/N \approx 4.7$, and find a best-fit ΛCDM parameter $\Omega_\Lambda \approx 0.83$ with tight uncertainties. The results are consistent with a cosmological constant ($w=-1$) and demonstrate a degeneracy between $w$ and $\Omega_\Lambda$ that ISW data alone cannot break. The work strengthens ΛCDM support and highlights the potential of future surveys (e.g., DES) to tighten constraints on dark energy.

Abstract

We cross-correlate the third-year WMAP data with galaxy samples extracted from the SDSS DR4 (SDSS4) covering 13% of the sky, increasing by a factor of 3.7 the volume sampled in previous analyses. The new measurements confirm a positive cross-correlation with higher significance (total signal-to-noise of about 4.7). The correlation as a function of angular scale is well fitted by the integrated Sachs-Wolfe (ISW) effect for LCDM flat FRW models with a cosmological constant. The combined analysis of different samples gives Omega_L=0.80-0.85$ (68% Confidence Level, CL) or $0.77-0.86$ (95% CL). We find similar best fit values for Omega_L for different galaxy samples with median redshifts of z ~0.3 and z ~0.5, indicating that the data scale with redshift as predicted by the LCDM cosmology (with equation of state parameter w=-1). This agreement is not trivial, but can not yet be used to break the degeneracy constraints in the w versus Omega_L plane using only the ISW data.

Cross-correlation of WMAP 3rd year and the SDSS DR4 galaxy survey: new evidence for Dark Energy

TL;DR

The paper tests the late ISW effect as evidence for dark energy by cross-correlating WMAP3 CMB temperature data with SDSS DR4 galaxy maps over ~13% of the sky. Using two galaxy subsamples and robust covariance analyses, the authors detect a significant cross-correlation with , and find a best-fit ΛCDM parameter with tight uncertainties. The results are consistent with a cosmological constant () and demonstrate a degeneracy between and that ISW data alone cannot break. The work strengthens ΛCDM support and highlights the potential of future surveys (e.g., DES) to tighten constraints on dark energy.

Abstract

We cross-correlate the third-year WMAP data with galaxy samples extracted from the SDSS DR4 (SDSS4) covering 13% of the sky, increasing by a factor of 3.7 the volume sampled in previous analyses. The new measurements confirm a positive cross-correlation with higher significance (total signal-to-noise of about 4.7). The correlation as a function of angular scale is well fitted by the integrated Sachs-Wolfe (ISW) effect for LCDM flat FRW models with a cosmological constant. The combined analysis of different samples gives Omega_L=0.80-0.850.77-0.86$ (95% CL). We find similar best fit values for Omega_L for different galaxy samples with median redshifts of z ~0.3 and z ~0.5, indicating that the data scale with redshift as predicted by the LCDM cosmology (with equation of state parameter w=-1). This agreement is not trivial, but can not yet be used to break the degeneracy constraints in the w versus Omega_L plane using only the ISW data.

Paper Structure

This paper contains 5 sections, 6 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. The Data
  3. Cross-Correlation and errors
  4. Comparison with Predictions
  5. Discussion

Figures (4)

  • Figure 1: SDSS DR4 galaxy density (LRG) fluctuation maps (right panel) compared to WMAP (V-band 3yr) temperature map (left panel). Both maps are smoothed with a Gaussian beam of FWHM $=0.3$ deg.
  • Figure 2: The continuous line with errorbars shows the WMAP3-SDSS4 angular cross-correlation as a function of scale for the $r=20-21$ sample (top) and the LRG sample (bottom). The dotted line corresponds to using the 1st yr WMAP (WMAP1-SDSS4) data, which is very close to the WMAP3 results (continuous line). The dashed lines show the $\Lambda$CDM model with $\Omega_\Lambda =0.83$ ( best overall fit) scaled to the appropriate bias and projected to each sample redshift.
  • Figure 3: Probability distribution: $1-P_\chi[>\Delta\chi^2,\nu=1]$ for $\Omega_\Lambda$ in the $r=20-21$ sample (short-dashed line), the LRG sample (long-dashed line) and the combined analysis (continuous middle curve). The range of $68\%$ and $95\%$ confidence regions in $\Omega_\Lambda$ are defined by the intersection with the corresponding horizontal lines.
  • Figure 4: Two dimensional contours for $\Omega_\Lambda$ and $w$, the DE effective equation of state. The inner black contour limits the 1D marginalized $68\%$ confidence region ($\Delta\chi^2=1$). The other contour correspond to $95\%$ limits ($\Delta\chi^2=4$).