The amplitude and spectral index of the large angular scale anisotropy in the cosmic microwave background radiation

In many cosmological models, the large angular scale anisotropy in the cosmic microwave background is parameterized by a spectral index, n, and a quadrupolar amplitude, Q. For a Harrison-Peebles-Zel'dovich spectrum, n = 1. Using data from the Far Infrared Survey (FIRS) and a new statistical measure, a contour plot of the likelihood for cosmological models for which -1 < n < 3 and 0 ≤ Q ≤ 50 μK is obtained. Depending upon the details of the analysis, the maximum likelihood occurs at n between 0.8 and 1.4 and Q between 18 and 21 μK. Regardless of Q, the likelihood is always less than half its maximum for n < -0.4 and for n > 2.2, as it is for Q < 8 μK and Q > 44 μK.