Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results

TL;DR

The nine-year WMAP study delivers final, beam-symmetry–corrected full-sky maps and a comprehensive analysis that tightly constrains the standard flat $ ext{LCDM}$ cosmology. By combining advanced map-making (including beam-symmetrized processing) with multiple foreground separation methods (ILC, MEM, MCMC, chi-squared) and a high-precision $C^{-1}$ power-spectrum estimator, the work yields precise cosmological parameters (e.g., $n_s=0.9608\pm0.0080$, $\Omega_k=-0.0027^{+0.0039}_{-0.0038}$, $H_0=69.32\pm0.80$) and robust inflationary support. Non-Gaussianity remains consistent with zero within tight bounds on $f_{NL}^{\rm loc}$, $f_{NL}^{\rm eq}$, and $f_{NL}^{\rm orth}$, while the data strongly favor a universe with nearly scale-invariant, adiabatic fluctuations and a predominantly cold dark matter component. The nine-year release also demonstrates the impact of beam asymmetry on certain statistics and confirms that the inflationary flat $ ext{LCDM}$ model provides a comprehensive description when combined with other cosmological probes, substantially reducing the viable parameter space. Overall, the final WMAP results solidify the standard cosmological model and establish a benchmark for subsequent CMB studies and cross-checks with external data sets.

Abstract

We present the final nine-year maps and basic results from the WMAP mission. We provide new nine-year full sky temperature maps that were processed to reduce the asymmetry of the effective beams. Temperature and polarization sky maps are examined to separate CMB anisotropy from foreground emission, and both types of signals are analyzed in detail. The WMAP mission has resulted in a highly constrained LCDM cosmological model with precise and accurate parameters in agreement with a host of other cosmological measurements. When WMAP data are combined with finer scale CMB, baryon acoustic oscillation, and Hubble constant measurements, we find that Big Bang nucleosynthesis is well supported and there is no compelling evidence for a non-standard number of neutrino species (3.84+/-0.40). The model fit also implies that the age of the universe is 13.772+/-0.059 Gyr, and the fit Hubble constant is H0 = 69.32+/-0.80 km/s/Mpc. Inflation is also supported: the fluctuations are adiabatic, with Gaussian random phases; the detection of a deviation of the scalar spectral index from unity reported earlier by WMAP now has high statistical significance (n_s = 0.9608+/-0.0080); and the universe is close to flat/Euclidean, Omega_k = -0.0027 (+0.0039/-0.0038). Overall, the WMAP mission has resulted in a reduction of the cosmological parameter volume by a factor of 68,000 for the standard six-parameter LCDM model, based on CMB data alone. For a model including tensors, the allowed seven-parameter volume has been reduced by a factor 117,000. Other cosmological observations are in accord with the CMB predictions, and the combined data reduces the cosmological parameter volume even further. With no significant anomalies and an adequate goodness-of-fit, the inflationary flat LCDM model and its precise and accurate parameters rooted in WMAP data stands as the standard model of cosmology.

Figures (44)

• Figure 1: The estimated level of artifacts ($\xi$) that would have occurred in the Ka-band map if no processing mask had been used. Band-dependent processing masks were used and tailored to minimize these artifacts when converting from time-ordered to sky map data. This map is in Galactic coordinates and the high intensity regions arise from observations when one of the beams is near the Galactic center and the processing mask is not used. (See Figure \ref{['fig:masks']} to compare with the analysis sky cuts.) Since bright artifacts originate primarily from beam crossings of bright Galactic plane regions, the nature of the unmasked artifact pattern is similar for all DAs. Although the patterns are similar for all bands, the highest amplitude artifacts occur in K- and Ka- bands because these have the brightest foregrounds. To prevent significant artifacts, processing masks are constructed for each band by growing the number of pixels in the mask until $\xi$ is sufficiently reduced. The estimated mean residual level of artifacts ($\overline{\xi}$) is given in Table \ref{['tab:masks_radii']}. We required $\overline{\xi}< 5\,\hbox{$\mu$\rm K}$ for all but K-band. Construction of the K-band mask is more complex (see text) yet still achieves $\overline{\xi} < 8\,\hbox{$\mu$\rm K}$. (A color version of this figure is available in the online journal.)
• Figure 2: Plots of the maximum and mean magnitude of the estimated map artifacts ($\xi$) for Ka-band versus the number of pixels masked by the processing mask. The vertical line indicates the adopted mask which is the smallest mask for which $\max(\xi) < 1.15~\xi^{max}_{sat}$ as described in the text.
• Figure 3: Nine-year temperature sky maps in Galactic coordinates shown in a Mollweide projection. Maps have been slightly smoothed with a $0\hbox{${\hbox{.}}^\circ$}2$ Gaussian beam. (A color version of this figure is available in the online journal.)
• Figure 4: Nine-year Stokes Q polarization sky maps in Galactic coordinates shown in a Mollweide projection. Maps have been smoothed to an effective Gaussian beam of $2\hbox{${\hbox{.}}^\circ$}0$. The smooth large angular scale features visible in W-band, and to a lesser extent in V-band, are the result of a pair of modes that are poorly constrained in map-making, yet properly de-weighted in the analysis. (A color version of this figure is available in the online journal.)
• Figure 5: Nine-year Stokes U polarization sky maps in Galactic coordinates shown in a Mollweide projection. Maps have been smoothed to an effective Gaussian beam of $2\hbox{${\hbox{.}}^\circ$}0$. The smooth large angular scale features visible in W-band, and to a lesser extent in V-band, are the result of a pair of modes that are poorly constrained in map-making, yet properly de-weighted in the analysis. (A color version of this figure is available in the online journal.)