Signal-to-Noise Eigenmode Analysis of the Two-Year COBE Maps

الأصل · EN

To test a theory of cosmic microwave background fluctuations, it is natural to expand an anisotropy map in an uncorrelated basis of linear combinations of pixel amplitudes --- statistically-independent for both the noise and the signal. These S/N-eigenmodes are indispensible for rapid Bayesian analyses of anisotropy experiments, applied here to the recently-released two-year COBE dmr maps and the firs map. A 2-parameter model with an overall band-power and a spectral tilt νΔₜ describes well inflation-based theories. The band-powers for all the dmr 53,90,31 a+b GHz and firs 170 GHz maps agree, {(1.1± 0.1)× 10⁻⁵}¹/², and are largely independent of tilt and degree of (sharp) S/N-filtering. Further, after optimal S/N-filtering, the dmr maps reveal the same tilt-independent large scale features and correlation function. The unfiltered dmr 53 a+b index νΔₜ+1 is 1.4± 0.4; increasing the S/N-filtering gives a broad region at (1.0--1.2)±0.5, a jump to (1.4--1.6)±0.5, then a drop to 0.8, the higher values clearly seen to be driven by S/N-power spectrum data points that do not fit single-tilt models. These indices are nicely compatible with inflation values (0.8--1.2), but not overwhelmingly so.