Power Spectrum of Primordial Inhomogeneity Determined from the FOUR-Year [ITAL]COBE[/ITAL] DMR Sky Maps

Abstract

Fourier analysis and power spectrum estimation of the cosmic microwave background anisotropy on an incompletely sampled sky developed by Górski has been applied to the 4 yr COBE DMR 31.5, 53, and 90 GHz sky maps. Likelihood analysis using newly constructed Galaxy cuts (extended beyond \b\ = 20° to excise the known foreground emission) and simultaneously correcting for the faint high-latitude Galactic foreground emission is conducted on the DMR sky maps pixelized in both ecliptic and Galactic coordinates. The Bayesian power spectrum estimation from the foreground-corrected 4 yr COBE DMR data renders n ̃ 1.2 ± 0.3 and Q_rms-PS ̃ 15.3_-2.8^+3.7 μK(projections of the two-parameter likelihood). The results are consistent with the Harrison-Zeldovich n = 1 model of amplitude Q_rms-PS ̃ 18 μK detected with significance exceeding 14 σ (δQ/Q ≲ 0.07). (A small power spectrum amplitude drop below the published 2 yr results is predominantly due to the application of the new, extended Galaxy cuts.).