Nonnucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters

Abstract

Because the baryon-to-photon ratio ?10 is in some doubt, we drop nucleosynthetic constraints on ?10 and fit the three cosmological parameters (h, ?M, ?10) to four observational constraints: Hubble parameter ho = 0.70 ? 0.15, age of the universe t=14 Gyr, cluster gas fraction fo ? fG h3/2 = 0.060 ? 0.006, and effective shape parameter ?o = 0.255 ? 0.017. Errors quoted are 1 ?, and we assume Gaussian statistics. We experiment with a fifth constraint ?o = 0.2 ? 0.1 from clusters. We set the tilt parameter n = 1 and the gas enhancement factor = 0.9. We consider cold dark matter models (open and ?M = 1) and flat ?CDM models. We omit HCDM models (to which the ?o constraint does not apply). We test goodness of fit and draw confidence regions by the ??2 method. CDM models with ?M = 1 (SCDM models) are accepted only because the large error on ho allows h < 0.5. Baryonic matter plays a significant role in ?o when ?M ~ 1. Open CDM models are accepted only for ?M 0.4. The combination of the four other constraints with ?o ? 0.2 is rejected in CDM models with 98% confidence, suggesting that light may not trace mass. ?CDM models give similar results. In all of these models, ?10 6 is favored strongly over ?10 2. This suggests that reports of low deuterium abundances on QSO lines of sight may be correct and that observational determinations of primordial 4He may have systematic errors. Plausible variations on n and in our models do not change the results much. If we drop or change the crucial ?o constraint, lower values of ?M and ?10 are permitted. The constraint ?o = 0.15 ? 0.04, derived recently from the IRAS redshift survey, favors ?M ? 0.3 and ?10 ? 5 but does not exclude ?10 ? 2.