Site Map
Follow us on Facebook Follow us on Twitter YouTube channel
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

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

>> PDF>> ADS

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.

Proceed on CAUP's website|Go to IA website