## 1. IntroductionThe standard picture of structure formation relies on the gravitational amplification of initially small perturbations in the matter distribution. The origin of these fluctuations is unclear, but a popular assumption is that these fluctuations originate in the very early universe during an inflationary epoch. The most straightforward incarnation of this inflationary scenario predicts that the fluctuations are adiabatic, Gaussian, Harrison-Zeldovich () and that the Universe is spatially flat (Kolb & Turner 1990). To avoid violating primordial nucleosynthesis constraints, the Universe should be dominated by non-baryonic matter. The cold dark matter (CDM) model has been the preferred model in the inflationary scenario (Peebles 1982, Liddle and Lyth, 1993). The statistical properties of CMB fluctuations provide an ideal tool for testing CDM models. CMB data offer valuable information not only on the scenario of the origin of cosmic structures, but also on the early physics of the Universe and the cosmological parameters that characterize the Universe. Using the CMB to determine these parameters is the beginning of a new era in cosmology. This truly cosmological method probes scales much larger and epochs much earlier () than more traditional techniques which rely on supernovae, galaxies, galaxy clusters and other low-redshift objects. The CMB probes the entire observable universe. Acoustic oscillations of the baryon-photon fluid at recombination produce peaks and valleys in the CMB power spectrum at sub-degree angular scales. Measurements of these model-dependent peaks and valleys have the potential to determine many important cosmological parameters to the few percent level (Jungman et al. 1996, Zaldarriaga et al. 1997). Within the next decade, increasingly accurate sub-degree scale CMB observations from the ground, from balloons and particularly from two new satellites (MAP: Wright et al. 1996, Planck Surveyor: Bersanelli et al. 1996) will tell us the ultimate fate of the Universe (), what the Universe is made of (, ) and the age and size of the Universe ()) with unprecedented precision. In preparation for the increasingly fruitful harvests of data, it
is important to determine what the combined CMB data can
In the present paper we focus on the range for Hubble's constant is possibly the most
important parameter in cosmology, giving the expansion rate, age and
size of the Universe. Recent, direct, low-redshift measurements fall
in the range [45-90] but may be subject to unidentified systematic
errors. Thus it is important to have different methods which may not
be subject to the same systematics. For example, CMB determinations of
The quantity is important because we would like to know what the Universe is made of and how much normal baryonic matter exists in it. The combination is relatively well-constrained by the observations and theory of primordial nucleosynthesis, but the uncertainty on the Hubble constant means that the value of is rather poorly constrained. The question of just how many baryons there are in the Universe has received close attention recently due to estimates of the baryon fraction in galaxy clusters and attempts to constrain by measuring the deuterium in high-redshift quasar absorption systems. The parameter The power spectrum quadrupole normalization We examine how the contraints on any one of these parameters change
as we condition on and marginalize over the other parameters. We
obtain minimization values and likelihood
intervals for All the results reported here were obtained under a restrictive set of assumptions. We assume inflation-based CDM models of structure formation with Gaussian adiabatic initial conditions in critical density universes () with no cosmological constant (). We have ignored the possibility of early reionization and any gravity wave contribution to the spectra. We do not test topological defect models. We use no hot dark matter. We have used the helium fraction and a mean CMB temperture K. Although we have not yet looked carefully at how dependent our results are on these assumptions we make some informed estimates in Sect. 6.1where we also discuss previous work using similar data sets and similar methods to look at different families of models. In Sect. 2we describe the data analysis. In Sect. 3we present our
results for © European Southern Observatory (ESO) 1998 Online publication: December 16, 1997 |