Baryonic mass fraction in rich clusters and the total mass density in the cosmos

Direct observations of the supposedly universal primordial deuterium abundance imply a relatively large baryon density Omega(B) = (0.019-0.030) h(-2) = (0.029-0.10) (95% confidence limit, hereafter CL) for Hubble constant H-o = 100 h = (70 +/- 15) km(-1) s(-1) Mpc(-1). From new observations of both the X-ray bremsstrahlung and the Sunyaev-Zeldovich effect, we obtain the baryon fraction in rich clusters, f(B) = (0.13 +/- 0.03)(62/H-o)(1.4). Together with the observed baryon density this implies that rich clusters are a fair sample of the universe (baryon enhancement Upsilon similar to 1) and that the cosmic total mass density Omega(m) = (0.3-0.9) (95% CL). This conclusion agrees with dynamical measures of Omega(m) on large scales. Conversely, this dynamically measured Omega(m) > 0.3 (2.4 sigma) and the rich cluster limit f(B) > 0.1 imply Omega(B) > 0.025 for h < 0.7, Upsilon similar to 1. This relatively large baryon density is consistent with standard big bang nucleosynthesis and some recent He-4 abundance observations.