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Centro de Astrofísica da Universidade do Porto

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

C. H. Lineweaver, D. Barbosa

Abstract
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 Ho, baryonic fraction ob , the spectral slope of scalar perturbations n and the power spectrum quadrupole normalization Q. We calculate chi (2) minimization values and likelihood intervals for these parameters. Within the models considered, a low value for the Hubble constant is preferred: Ho= 30(+18}_{-7) :km s(-1}Mpc({-1)) . The baryonic fraction is not as well-constrained by the CMB data: Omega_ {b}= 0.07({+) 0.24}_{-0.07}. The power spectrum slope is n =0.91(+0.20}_{-0.12) . The power spectrum normalization is Q=18 +/- 2.5:mu K. % The error bars on each parameter are approximately 1sigma and are for the case where the other 3 parameters have been marginalized. If we condition on n=1 we obtain the normalization Q= 17 +/- 1.0:mu 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-Ho 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.

Astronomy and Astrophysics
Volume 329, Page 799
January 1998

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