1998ApJ...508..535B

Direct observations of the supposedly universal primordial deuterium abundance imply a relatively large baryon density Ω_B = (0.019-0.030) h^–2 = (0.029-0.10) (95% confidence limit, hereafter CL) for Hubble constant H₀ ≡ 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/H₀)^1.4. Together with the observed baryon density this implies that rich clusters are a fair sample of the universe (baryon enhancement Υ ∼ 1) and that the cosmic total mass density Ω_m_ = (0.3-0.9) (95% CL). This conclusion agrees with dynamical measures of Ω_m on large scales. Conversely, this dynamically measured Ω_m > 0.3 (2.4 σ) and the rich cluster limit f_B_ > 0.1 imply Ω_B > 0.025 for h < 0.7, Υ ∼ 1. This relatively large baryon density is consistent with standard big bang nucleosynthesis and some recent ⁴He abundance observations.