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Centro de Astrofísica da Universidade do Porto

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

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

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 Ωb, and the cosmological constant λ0. We fit h-, Ωb- and λ0-dependent power spectra to the data. The models 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-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 qo 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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