Omega baryon via Oort's Method

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The baryon density of the universe is equal to the product of the baryon-to-light ratio, Mb/L, and the luminosity density, j. We estimate Mb/L as the sum of the masses of the X-ray gas and the visible stars in a rich cluster of galaxies divided by the luminosity of the cluster galaxies in precisely the same sky aperture. We evaluate the gas-to-light ratio derived from the EMSS detect cell flux and the CNOC cluster redshift survey galaxies. After making an aperture correction to an effective overdensity of 500rhoc, we find that Omegagas=0.012-0.016 h-3/2, depending on the galaxy fading correction. Adding in the galaxy baryons at a mass-to-light ratio of 5 Msun/Lsun, equivalent to Omegaₛtars=0.003h-1, we find that Omegab=0.015-0.019 for H₀=100 (or 0.040-0.051 for H₀=50). Expressed as the baryon to photon ratio, eta, this corresponds to eta=4.0-5.2x10⁻¹⁰ (H₀=100) and is in the mid-range of values from other methods. The individual clusters have a dispersion about the mean Omegagas of 40%, and the chi² of the 14 clusters is consistent with the hypothesis that the gas-to-light ratio is a universal constant. If we ignore the light of the cD, the variance increases by a factor of three. After the radial segregation of gas and light within a cluster is taken into account, these statistics indicate that there is little variation of the gas-to-light ratio from cluster to cluster over the 0.2 to 0.55 range in redshift.