Cosmology from cosmic microwave background and galaxy clusters

We present the results of analysis of constraints on cosmological parameter s from cosmic microwave background (CMB) alone and in combination with the galaxy cluster baryon fraction assuming inflation-generated adiabatic scala r fluctuations. The CMB constraints are obtained using our likelihood appro ximation method (Bartlett et al. 2000; Douspis et al. 2001). In the present analysis we use the new data coming from MAXIMA and BOOMERanG balloon-born e experiments and the first results of the DASI interferometer together wit h the COBE/DMR data. The quality of these independent data sets implies tha t the C-l are rather well known, and allow reliable constraints. We found t hat the constraints in the Omega - H-0 plane are very tightened, favouring a at Universe, that the index of the primordial fluctuations is very close to one, that the primordial baryon density is now in good agreement with pr imordial nucleosynthesis. Nevertheless degeneracies between several paramet ers still exist, and for instance the constraint on the cosmological consta nt or the Hubble constant are very weak, preferred values being low. A way to break these degeneracies is to "cross-constrain" the parameters by combi ning them with constraints from other independent data. We use the baryon f raction determination from X-ray clusters of galaxies as an additional cons traint and show that the combined analysis leads to strong constraints on a ll cosmological parameters. Using a high baryon fraction (similar to 15% fo r h = 0.5) we found a rather low Hubble constant, values around 80 km s(-1) /Mpc being ruled out. Using a recent and low baryon fraction estimation (si milar to 10% for h = 0.5) we found a preferred model with a low Hubble cons tant and a high density content (Omega (m)), an Einstein-de Sitter model be ing only weakly ruled out.