The intracluster gas fraction in X-ray clusters: constraints on the clustered mass density

The mean intracluster gas fraction of X-ray clusters within their hydrostatic regions is derived from recent observational compilations of David, Jones & Forman and White & Fabian. At radii encompassing a mean density 500 times the critical value, the individual sample bi-weight means are moderately (2. 4 by numerical simulations removes the discrepancy and results in a combined sample mean and standard error \ (r₅₀₀) = (0. 060 \ 0. 003) assumption to maximize cluster gas content, this value constrains the universal ratio of total, clustered to baryonic mass \ₘ/\b \ 23. 1 physically plausible approach based on low D/H inferences from quasar absorption spectra and accounting for baryons within cluster galaxies yields an estimate Ømegaₘ \^2/3 = 0. 28 \ 0. 07 with sources of systematic error involved in the derivation providing approximately 35% uncertainty. Additional effects which could provide consistency with the Einstein-deSitter case Ømegaₘ \ 1 are presented, and their observable signatures discussed.