First Year Wilkinson Microwave Anisotropy Probe (WMAP1) Observations: The Angular Power Spectrum

We present the angular power spectrum derived from the first-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power spectrum estimation methods and data combinations and demonstrate that the results are robust. The data are modestly contaminated by diffuse Galactic foreground emission, but we show that a simple Galactic template model is sufficient to remove the signal. Point sources produce a modest contamination in the low frequency data. After masking 700 known bright sources from the maps, we estimate residual sources contribute 3500 K2 at 41 GHz, and 130 K2 at 94 GHz, to the power spectrum [l(l + 1)Cl 2 ] at l = 1000. Systematic errors are negligible compared to the (modest) level of foreground emission. Our best estimate of the power spectrum is derived from 28 cross-power spectra of statistically independent channels. The final spectrum is essentially independent of the noise properties of an individual radiometer. The resulting spectrum provides a definitive measurement of the CMB power spectrum, with uncertainties limited by cosmic variance, up to l 350. The spectrum clearly exhibits a first acoustic peak at l = 220 and a second acoustic peak at l 540 (Page et al. 2003b), and it provides strong support for adiabatic initial conditions (Spergel et al. 2003). Kogut et al. (2003) analyze the CT E l power spectrum, and present evidence for a relatively high optical depth, and an early period of cosmic reionization. Among other things, this implies that the temperature power spectrum has been suppressed by 30% on degree angular scales, due to secondary scattering. Subject headings: cosmic microwave background, cosmology: observations, early universe, space vehicles: instruments 1WMAP 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. 2Code 685, Goddard Space Flight Center, Greenbelt, MD 20771 3Dept of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 4Science Systems and Applications, Inc. (SSAI), 10210 Greenbelt Road, Suite 600 Lanham, Maryland 20706 5Depts. of Astrophysics and Physics, EFI and CfCP, University of Chicago, Chicago, IL 60637 6Dept. of Physics, Jadwin Hall, Princeton, NJ 08544 7Dept. of Physics and Astronomy, University of British Columbia, Vancouver, BC Canada V6T 1Z1 8National Research Council (NRC) Fellow 9Dept. of Physics, Brown University, Providence, RI 02912 10UCLA Astronomy, PO Box 951562, Los Angeles, CA 90095-1562