SEVEN-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE (WMAP) OBSERVATIONS: SKY MAPS, SYSTEMATIC ERRORS, AND BASIC RESULTS

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(b)h(2) = 0.02260 +/- 0.00053, Omega(c)h(2) = 0.1123 +/- 0.0035, Omega(Lambda) = 0.728(-0.016)(+0.015), 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 l less than or similar to 919, allowing a robust measurement of the third acoustic peak. This measurement results in improved constraints on the matter density, Omega(m)h(2) = 0.1334(-0.0055)(+0.0056), and the epoch of matter-radiation equality, z(eq) = 3196(-133)(+134), using WMAP data alone. The new WMAP data, when combined with smaller angular scale microwave background anisotropy data, result in a 3 sigma detection of the abundance of primordial helium, Y-He = 0.326 +/- 0.075. When combined with additional external data sets, the WMAP data also yield better determinations of the total mass of neutrinos, Sigma m(nu) <= 0.58 eV (95% CL), and the effective number of neutrino species, N-eff = 4.34(-0.88)(+0.86). 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.