ar X iv : a st ro - p h / 03 02 20 7 v 2 1 2 Fe b 20 03 First Year Wilkinson Microwave Anisotropy Probe ( WMAP 1 ) Observations : Preliminary Maps and Basic Results

We present full sky microwave maps in five frequency bands (23 to 94 GHz) from the WMAP first year sky survey. Calibration errors are <0.5% and the low systematic error level is well specified. The cosmic microwave background (CMB) is separated from the foregrounds using multifrequency data. The sky maps are consistent with the 7◦ full-width at half-maximum (FWHM) Cosmic Background Explorer (COBE) maps. We report more precise, but consistent, dipole and quadrupole values. The CMB anisotropy obeys Gaussian statistics with −58 < fNL < 134 (95% CL). The 2 ≤ l ≤ 900 anisotropy power spectrum is cosmic variance limited for l < 354 with a signal-tonoise ratio >1 per mode to l = 658. The temperature-polarization cross-power spectrum reveals both acoustic features and a large angle correlation from reionization. The optical depth of reionization is τ = 0.17±0.04, which implies a reionization epoch of tr = 180 −80 Myr (95% CL) after the Big Bang at a redshift of zr = 20 +10 −9 (95% CL) for a range of ionization scenarios. This early reionization is incompatible with the presence of a significant warm dark matter density. A best-fit cosmological model to the CMB and other measures of large scale structure works remarkably well with only a few parameters. The age of the best-fit universe is t0 = 13.7±0.2 Gyr old. Decoupling was tdec = 379 +8 −7 kyr after the Big Bang at a redshift of zdec = 1089± 1. The thickness of the decoupling surface was ∆zdec = 195 ± 2. The matter density of the universe is Ωmh 2 = 0.135 −0.009, the baryon density is Ωbh 2 = 0.0224± 0.0009, and the total mass-energy of the universe is Ωtot = 1.02± 0.02. There is progressively less fluctuation power on smaller scales, from WMAP to fine scale CMB measurements to galaxies and finally to the Ly-α forest. This is accounted for with a running spectral index, significant at the ∼ 2σ level. The spectral index of WMAP is the result of a partnership between Princeton University and NASA’s Goddard Space Flight Center. Scientific guidance is provided by the WMAP Science Team. Code 685, Goddard Space Flight Center, Greenbelt, MD 20771 Dept. of Physics and Astronomy, University of British Columbia, Vancouver, BC Canada V6T 1Z1 Dept. of Physics, Jadwin Hall, Princeton, NJ 08544 National Research Council (NRC) Fellow Depts. of Astrophysics and Physics, EFI and CfCP, University of Chicago, Chicago, IL 60637 Dept of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 Dept. of Physics, Brown University, Providence, RI 02912 UCLA Astronomy, PO Box 951562, Los Angeles, CA 90095-1562 Science Systems and Applications, Inc. (SSAI), 10210 Greenbelt Road, Suite 600 Lanham, Maryland 20706