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Astron. Astrophys. 329, 799-808 (1998)

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Cosmic microwave background observations:
implications for Hubble's constant and the spectral parameters n
and Q in cold dark matter critical density universes

Charles H. Lineweaver 1 and Domingos Barbosa 1, 2

1 Observatoire astronomique de Strasbourg, U.L.P., F-67000 Strasbourg, France.
2 Centro de Astrofsica da U.P., Rua do Campo Alegre 823, PT-4150 Porto, Portugal.

Received 2 December 1996 / Accepted 21 May 1997


Recent cosmic microwave background (CMB) measurements over a large range of angular scales have become sensitive enough to provide interesting constraints on cosmological parameters within a restricted class of models. We use the CMB measurements to study inflation-based, cold dark matter (CDM) critical density universes. We explore the 4-dimensional parameter space having as free parameters, Hubble's constant [FORMULA], baryonic fraction [FORMULA], the spectral slope of scalar perturbations n and the power spectrum quadrupole normalization Q. We calculate [FORMULA] minimization values and likelihood intervals for these parameters. Within the models considered, a low value for the Hubble constant is preferred: [FORMULA]. The baryonic fraction is not as well-constrained by the CMB data: [FORMULA]. The power spectrum slope is [FORMULA]. The power spectrum normalization is [FORMULA] K. The error bars on each parameter are approximately [FORMULA] and are for the case where the other 3 parameters have been marginalized. If we condition on [FORMULA] we obtain the normalization [FORMULA] K. The permitted regions of the 4-D parameter space are presented in a series of 2-D projections. In the context of the CDM critical density universes considered here, current CMB data favor a low value for the Hubble constant. Such low- [FORMULA] models are consistent with Big Bang nucleosynthesis, cluster baryonic fractions, the large-scale distribution of galaxies and the ages of globular clusters; although in disagreement with direct determinations of the Hubble constant.

Key words: cosmic microwave background – cosmology: observations – theory

Send offprint requests to: Charley Lineweaver,

© European Southern Observatory (ESO) 1998

Online publication: December 16, 1997