Cosmic Microwave Background Observations: Implications for Hubble’s Constant and the Spectral Parameters n and Q

Recent cosmic microwave background (CMB) measurements over a large range of angular scales have become sensitive enough to provide interesting constraints on cosmological parameters. In the context of adiabatic perturbations in critical density universes, we use CMB measurements to explore the 4-dimensional parameter space having as free parameters Hubble’s constant Ho, baryonic fraction Ωb, the spectral slope of scalar perturbations n and the power spectrum quadrupole normalization Q. We calculate χ minimization values and likelihood intervals for these parameters. We obtain a low value for Hubble’s constant: Ho = 30 +13 −9 km s Mpc. The baryonic fraction is not well constrained by the CMB data. The power spectrum slope is n = 0.93 −0.16. The power spectrum normalization is Q = 17.5 −2.5 μK. These results include estimated uncertainties due to the Saskatoon calibration uncertainty. The error bars on each parameter are for the case where the other 3 parameters have been marginalized. If we condition on n = 1 we obtain the normalization Q = 17 −2 μK. The permitted regions of the 4-D parameter space are presented in a series of 2-D projections. Without the CMB data, the combined limits from big bang nucleosynthesis, cluster baryonic fractions and the large scale density fluctuation shape parameter Γ (in the context of cold dark matter Ωo = 1, λo = 0 models) yield, Ho ≈ 35 +6 −5 km s Mpc. For these same cold dark matter models, the CMB data provide a measurement consistent with such a low value for Ho.