Constraints on h, Ω _b and λ ₀ from cosmic microwave background observations

C. H. Lineweaver, D. Barbosa, A. Blanchard, J.G. Bartlett

Abstract
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 fraction Ω_b, and the cosmological constant λ₀. We fit h-, Ω_b- and λ₀-dependent power spectra to the data. The models we consider are flat cold dark matter (CDM) dominated universes with flat (n_s=1) power spectra, thus the results obtained apply only to these models. CMB observations can exclude more than half of the h-Ω_b parameter space explored. The CMB data favor low values of Hubble's constant; h=~0.35. Low values of Ω_b are preferred (Ω_b~0.03) but the χ₂ minimum is shallow and we obtain Ω_b<0.28. A model with h=~0.40, Ω_b=~0.15 and Ω_cdm=~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-λ₀ models, the CMB data, combined with BBN constraints exclude most of the h-λ₀ plane. Models with Ω₀=~0.3, λ₀=~0.7 with h=~0.75 are fully consistent with the CMB data but are excluded by the strict new q_o limits from supernovae (Perlmutter et al. 1997). A combination of CMB data goodness-of-fit statistics, BBN and supernovae constraints in the h-λ₀ plane, limits Hubble's constant to the interval 0.23<0.72.

Astronomy and Astrophysics
Volume 322, Page 365
June 1997

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