Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Sky Maps, Systematic Errors, and Basic Results

TL;DR

This paper presents the WMAP seven-year full-sky temperature and polarization maps across five frequency bands, detailing data-processing updates, beam modeling refinements, and advanced map-making with asymmetric masking. It demonstrates that the seven-year data are consistent with, yet more constraining than, earlier releases, yielding tighter cosmological parameters within a minimal flat $\Lambda$CDM framework and enabling precise inferences such as $n_s=0.963\pm0.012$ and a primordial helium abundance $Y_{\rm He}=0.326\pm0.075$ from CMB data combined with external probes. The work emphasizes improved instrument characterizations (beam transfer functions, solid angles), robust null tests for low-$\ell$ polarization, and the public availability of high-fidelity sky maps and derived products for broader cosmological analyses. Overall, the seven-year release tightens constraints on fundamental parameters, strengthens tests of Big Bang cosmology, and showcases methodological advances in CMB data processing and analysis.

Abstract

(Abridged) New full sky temperature and polarization maps based on seven years of data from WMAP are presented. The new results are consistent with previous results, but have improved due to reduced noise from the additional integration time, improved knowledge of the instrument performance, and improved data analysis procedures. The improvements are described in detail. The seven year data set is well fit by a minimal six-parameter flat Lambda-CDM model. The parameters for this model, using the WMAP data in conjunction with baryon acoustic oscillation data from the Sloan Digital Sky Survey and priors on H_0 from Hubble Space Telescope observations, are: Omega_bh^2 = 0.02260 +-0.00053, Omega_ch^2 = 0.1123 +-0.0035, Omega_Lambda = 0.728 +0.015 -0.016, n_s = 0.963 +-0.012, tau = 0.087 +-0.014 and sigma_8 = 0.809 +-0.024 (68 % CL uncertainties). The temperature power spectrum signal-to-noise ratio per multipole is greater that unity for multipoles < 919, allowing a robust measurement of the third acoustic peak. This measurement results in improved constraints on the matter density, Omega_mh^2 = 0.1334 +0.0056 -0.0055, and the epoch of matter- radiation equality, z_eq = 3196 +134 -133, using WMAP data alone. The new WMAP data, when combined with smaller angular scale microwave background anisotropy data, results in a 3 sigma detection of the abundance of primordial Helium, Y_He = 0.326 +-0.075.The power-law index of the primordial power spectrum is now determined to be n_s = 0.963 +-0.012, excluding the Harrison-Zel'dovich-Peebles spectrum by >3 sigma. These new WMAP measurements provide important tests of Big Bang cosmology.

Figures (9)

• Figure 1: Measurements of the year-to-year calibration variation for K, Ka and Q bands obtained by correlating the Galactic plane signal in the seven-year map to the signal in single year sky maps. Note that the measured variations are consistent with the estimated absolute calibration uncertainty of 0.2%. No significant variation is seen for the V and W band maps.
• Figure 2: Physical optics beam models for the W1 DA on the A side (left) and B side (right) of the WMAP instrument. The ordinate is scaled by a $\sinh^{-1}$ function that provides a smooth transition between linear and logarithmic regimes. Blue: five-year models; red: seven-year models. Points: seven-year Jupiter beam data averaged in radial bins of $\Delta r = 0\farcm5$. Dashed lines: Radii at which hybrid beam profiles consist of 90%, 50%, and 10% Jupiter data, respectively, from smaller to larger radii. Model differences inside $r\sim1\fdg7$ are mostly suppressed in the hybrid beam profiles, whereas model differences outside $r\sim2\fdg6$ are mostly retained.
• Figure 3: W1 hybrid beam profiles from five-year (blue) and seven-year (red) analysis, combined for the A and B sides. The ordinate is scaled by a $\sinh^{-1}$ function that provides a smooth transition between linear and logarithmic regimes. Dashed lines: Radii at which hybrid beam profiles consist of 90%, 50%, and 10% Jupiter data, respectively, from smaller to larger radii. The noise shows that use of Jupiter data extends effectively to larger radii in the seven-year analysis.
• Figure 4: Comparison of beam transfer functions and uncertainties between five-year and seven-year analyses. Black: Relative change in beam transfer functions from five to seven years in the sense $(\textrm{7 yr}-\textrm{5 yr})/(\textrm{5 yr})$. Green: five-year $1\sigma$ error envelope. Red: seven-year $1\sigma$ error envelope. The seven-year $b_\ell$ are largely within $1\sigma$ of the five-year $b_\ell$, while the change in the error envelope itself is small. In W band, modeling differences between the A and B sides introduce an increase in the uncertainty plateau for multipoles $\ell \lesssim 1000$, whereas the small angle (high $\ell$) uncertainty is decreased for all bands.
• Figure 5: Plots of the Stokes I maps in Galactic coordinates. The left column displays the seven-year average maps, all of which have a common dipole signal removed. The right column displays the difference between the seven-year average maps and the previously published five-year average maps, adjusted to take into account the slightly different dipoles subtracted in the seven-year and five-year analyses and the slightly differing calibrations. All maps have been smoothed with a $1^{\circ}$ FWHM Gaussian kernel. The small Galactic plane signal in the difference maps arises from the difference in calibration ($0.1\%$) and beam symmetrization between the five-year and seven-year processing. Note that the temperature scale has been expanded by a factor of 20 for the difference maps.