Ωb and λo from cosmic microwave background observations

In this paper we compare data to theory. We use a compilation of the most recent cosmic microwave background (CMB) measurements to constrain Hubble’s constant h, the baryon fractionΩb, and the cosmological constant λo. We fit h-, Ωband λo-dependent power spectra to the data. Themodels we consider are flat cold dark matter (CDM) dominated universes with flat (ns = 1) power spectra, thus the results obtained apply only to these models. CMB observations can exclude more than half of the h − Ωb parameter space explored. The CMB data favor low values of Hubble’s constant; h ≈ 0.35. Low values of Ωb are preferred (Ωb ∼ 0.03) but the χ2 minimum is shallow and we obtain Ωb < 0.28. A model with h ≈ 0.40, Ωb ≈ 0.15 and Ωcdm ≈ 0.85 is permitted by constraints from the CMB data, BBN, cluster baryon fractions and the shape parameter Γ derived from the mass density power spectra of galaxies and clusters. For flat-λo models, the CMB data, combined with BBN constraints excludemost of the h−λo plane.Models withΩo ≈ 0.3, λo ≈ 0.7 with h ≈ 0.75 are fully consistent with the CMB data but are excluded by the strict new qo limits from supernovae (Perlmutter et al. 1997). A combination of CMB data goodnessof-fit statistics, BBN and supernovae constraints in the h − λo plane, limits Hubble’s constant to the interval 0.23 < h < 0.72.