Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Data Processing, Sky Maps, and Basic Results

TL;DR

The five-year WMAP analysis delivers improved full-sky temperature and polarization maps across 23–94 GHz with refined calibration and beam modeling, enabling stringent tests of ΛCDM and tighter cosmological constraints. By integrating additional years of data and a deeper understanding of instrument response, the paper reports precise measurements of key parameters such as $\Omega_b h^2$, $\Omega_c h^2$, $n_s$, and $\tau$, and places strong limits on $r$ and $N_{\rm eff}$ that support a nearly flat, adiabatic, Gaussian universe with a modest neutrino contribution. The results remain consistent with ΛCDM when combined with BAO and SNe data, while Ka-band polarization improves sensitivity and supports the inclusion of polarization data in cosmological analyses. The work also delivers substantial methodological advances in calibration, beam modeling, foreground treatment, and data products, fostering robust future analyses using LAMBDA resources.

Abstract

We present new full-sky temperature and polarization maps in five frequency bands from 23 to 94 GHz, based on data from the first five years of the WMAP sky survey. The five-year maps incorporate several improvements in data processing made possible by the additional years of data and by a more complete analysis of the instrument calibration and in-flight beam response. We present several new tests for systematic errors in the polarization data and conclude that Ka band data (33 GHz) is suitable for use in cosmological analysis, after foreground cleaning. This significantly reduces the overall polarization uncertainty. With the 5 year WMAP data, we detect no convincing deviations from the minimal 6-parameter LCDM model: a flat universe dominated by a cosmological constant, with adiabatic and nearly scale-invariant Gaussian fluctuations. Using WMAP data combined with measurements of Type Ia supernovae and Baryon Acoustic Oscillations, we find (68% CL uncertainties): Omega_bh^2 = 0.02267 \pm 0.00059, Omega_ch^2 = 0.1131 \pm 0.0034, Omega_Lambda = 0.726 \pm 0.015, n_s = 0.960 \pm 0.013, tau = 0.084 \pm 0.016, and Delta_R^2 = (2.445 \pm 0.096) x 10^-9. From these we derive: sigma_8 = 0.812 \pm 0.026, H_0 = 70.5 \pm 1.3 km/s/Mpc, z_{reion} = 10.9 \pm 1.4, and t_0 = 13.72 \pm 0.12 Gyr. The new limit on the tensor-to-scalar ratio is r < 0.22 (95% CL). We obtain tight, simultaneous limits on the (constant) dark energy equation of state and spatial curvature: -0.14 < 1+w < 0.12 and -0.0179 < Omega_k < 0.0081 (both 95% CL). The number of relativistic degrees of freedom (e.g. neutrinos) is found to be N_{eff} = 4.4 \pm 1.5, consistent with the standard value of 3.04. Models with N_{eff} = 0 are disfavored at >99.5% confidence.

Figures (13)

• Figure 1: Five-year temperature sky maps in Galactic coordinates smoothed with a $0.2\hbox{$^{\circ}$}$ Gaussian beam, shown in Mollweide projection. top: K band (23 GHz), middle-left: Ka band (33 GHz), bottom-left: Q band (41 GHz), middle-right: V band (61 GHz), bottom-right: W band (94 GHz).
• Figure 2: Five-year Stokes Q polarization sky maps in Galactic coordinates smoothed to an effective Gaussian beam of $2.0\hbox{$^{\circ}$}$, shown in Mollweide projection. top: K band (23 GHz), middle-left: Ka band (33 GHz), bottom-left: Q band (41 GHz), middle-right: V band (61 GHz), bottom-right: W band (94 GHz).
• Figure 3: Five-year Stokes U polarization sky maps in Galactic coordinates smoothed to an effective Gaussian beam of $2.0\hbox{$^{\circ}$}$, shown in Mollweide projection. top: K band (23 GHz), middle-left: Ka band (33 GHz), bottom-left: Q band (41 GHz), middle-right: V band (61 GHz), bottom-right: W band (94 GHz).
• Figure 4: Five-year polarization sky maps in Galactic coordinates smoothed to an effective Gaussian beam of $2.0\hbox{$^{\circ}$}$, shown in Mollweide projection. The color scale indicates polarized intensity, $P = \sqrt{Q^2+U^2}$, and the line segments indicate polarization direction in pixels whose signal-to-noise exceeds 1. top: K band (23 GHz), middle-left: Ka band (33 GHz), bottom-left: Q band (41 GHz), middle-right: V band (61 GHz), bottom-right: W band (94 GHz).
• Figure 5: Difference between the 5 year and 3 year temperature maps. left column: the difference in the maps, as delivered, save for the subtraction of a relative offset (Table \ref{['tab:i_diff']}), right column: the difference after correcting the 3 year maps by a scale factor that accounts for the mean gain change, $\sim 0.3$%, between the 3 year and 5 year estimates. top to bottom: K, Ka, Q, V, W band. The differences before recalibration are dominated by galactic plane emission and a dipole residual: see Table \ref{['tab:i_diff']}, which also gives the changes for $l=2,3$.