First‐Year <i>Wilkinson Microwave Anisotropy Probe</i> ( <i>WMAP</i> ) Observations: The Angular Power Spectrum

Abstract

We present the angular power spectrum derived from the first-year Wilkinson\nMicrowave Anisotropy Probe (WMAP) sky maps. We study a variety of power\nspectrum estimation methods and data combinations and demonstrate that the\nresults are robust. The data are modestly contaminated by diffuse Galactic\nforeground emission, but we show that a simple Galactic template model is\nsufficient to remove the signal. Point sources produce a modest contamination\nin the low frequency data. After masking ~700 known bright sources from the\nmaps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130\nuK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic\nerrors are negligible compared to the (modest) level of foreground emission.\nOur best estimate of the power spectrum is derived from 28 cross-power spectra\nof statistically independent channels. The final spectrum is essentially\nindependent of the noise properties of an individual radiometer. The resulting\nspectrum provides a definitive measurement of the CMB power spectrum, with\nuncertainties limited by cosmic variance, up to l~350. The spectrum clearly\nexhibits a first acoustic peak at l=220 and a second acoustic peak at l~540 and\nit provides strong support for adiabatic initial conditions. Kogut et al.\n(2003) analyze the C_l^TE power spectrum, and present evidence for a relatively\nhigh optical depth, and an early period of cosmic reionization. Among other\nthings, this implies that the temperature power spectrum has been suppressed by\n\\~30% on degree angular scales, due to secondary scattering.\n