Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results (1212.5225v3)

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.

• The paper presents precise CMB anisotropy measurements that refine cosmological parameters and support the standard ΛCDM model.
• It applies advanced power spectrum analysis methods, including optimal C⁻¹ and MASTER techniques, to achieve high-accuracy multipole estimations.
• Foreground analysis distinguishes Galactic emissions effectively, constraining key factors like the universe’s age, Hubble constant, and neutrino properties.

Overview of the Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations

The paper, "Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results," presents comprehensive results from the nine-year WMAP mission, focusing on the final maps and resultant cosmological inferences. The mission has substantially refined the measurements of the cosmic microwave background (CMB) anisotropies, enabling highly precise cosmological parameter estimations. The dataset's depth and breadth have allowed for a complex analysis of the CMB, synthesizing with other astrophysical data to test and reinforce the $\Lambda$CDM model as the standard cosmological framework.

Key Results and Methodologies

1. Power Spectrum Analysis: Using a combination of optimal $C^{-1}$ estimation methods and the more traditional MASTER method, the paper provides a temperature-temperature (TT) power spectrum that covers multipoles from $l = 2$ to $l = 1200$. A significant result here is the alignment and amplitude of the quadrupole and octupole moments, which are inline with theoretical predictions when cosmic variance and uncertainties in foreground removal are considered.
2. Cosmological Parameters: The analysis has led to parameters for a six-parameter $\Lambda$CDM model. The findings include constraints such as the spectral index, $n_s = 0.9608 \pm 0.0080$, indicating a deviation from unity, a measure of inflationary models' tilt. The age of the universe is cited at $13.772 \pm 0.059$ Gyr, with the Hubble constant, $H_0 = 69.32 \pm 0.80$ km/s/Mpc, and a well-supported Big Bang nucleosynthesis with $N_{\rm eff} = 3.84 \pm 0.40$, finding no evidence for additional neutrino species.
3. Foreground Analysis: A significant part of the research is focused on distinguishing CMB anisotropies from Galactic and extragalactic foreground emissions. Various methods, including Maximum Entropy Method (MEM), Markov Chain Monte Carlo (MCMC), and $\chi^2$ fitting, were used to characterize synchrotron, free-free, spinning dust, and thermal dust contributions. The spinning dust component is particularly notable, with a peak frequency below the available WMAP frequency bands, indicating significant sub-GHz influences.
4. Implications for Non-Gaussianity: Attempts to assess primordial non-Gaussianity using bispectra methods show no significant deviations from Gaussian statistics, though some evaluations suggest marginal local-like and orthogonal deviations. $f_{NL}^{\rm loc}$ is constrained to be within $-3 < f_{NL}^{\rm loc} < 77$ at 95% confidence, reinforcing the inflationary model's predictions with some uncertainty remaining.

Implications and Future Directions

WMAP's nine-year dataset substantially consolidates the $\Lambda$CDM model, particularly regarding the universe's curvature, age, and the dark matter/energy proportions. This dataset reduces the allowed cosmological model volume by a factor of 68,000 compared to pre-WMAP data, representing an unprecedented precision in cosmology. Future experiments, such as those by Planck, promise to provide even more stringent constraints, potentially illuminating even subtler properties of the universe's early conditions and validating the current cosmological model with greater fidelity.

This work confirms the critical role of CMB observations in cosmology, offering insights that are indispensable for understanding both the universe's large-scale structure and its minute fluctuations. Continued analysis and combination with other cosmological data remain vital for testing the foundations and predictions of cosmological theories further, with WMAP's mission forming a critical baseline for these future explorations.