paper

The Intracluster Gas Fraction in X-ray Clusters : Constraints on the Clustered Mass Density

arXiv:astro-ph/9701148 · doi:10.1093/mnras/292.2.289

Abstract

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 () discrepant; revising binding masses with a virial relation calibrated by numerical simulations removes the discrepancy and results in a combined sample mean and standard error $\fbargas(r_{500}) = (0.060 \pm 0.003) \h^{-3/2}$. For hierarchical clustering models with an extreme physical assumption to maximize cluster gas content, this value constrains the universal ratio of total, clustered to baryonic mass $Ω_m/Ω_b \le 23.1 \h^{3/2}$; combining with the primordial nucleosynthesis upper limit on results in $Ω_m \h^{1/2} < 0.60$. A less conservative, physically plausible approach based on low D/H inferences from quasar absorption spectra and accounting for baryons within cluster galaxies yields an estimate $Ω_m \h^{2/3} = 0.28 \pm 0.07$ with sources of systematic error involved in the derivation providing approximately uncertainty. Additional effects which could provide consistency with the Einstein-deSitter case $Ω_m \se 1$ are presented, and their observable signatures discussed.

8 pages, MN style, 2 epfs figures included. Submitted to MNRAS

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