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Using sensitive centimeter-wave receivers mounted on the Owens Valley Radio Observatory and Berkeley-Illinois-Maryland-Association millimeter arrays, we have obtained interferometric measurements of the Sunyaev-Zeldovich (SZ) effect toward massive galaxy clusters. We use the SZ data to determine the pressure distribution of the cluster gas and, in combination with published X-ray temperatures, to infer the gas mass and total gravitational mass of 18 clusters. The gas mass fraction, fg, is calculated for each cluster and is extrapolated to the fiducial radius r500 using the results of numerical simulations. The mean fg within r500 is 0.081^{+0.009}_{-0.011} h_100^{-1} (statistical uncertainty at 68% confidence level, assuming Omega_M = 0.3, Omega_L = 0.7). We discuss possible sources of systematic errors in the mean fg measurement. We derive an upper limit for Omega_M from this sample under the assumption that the mass composition of clusters within r500 reflects the universal mass composition: Omega_M h <= Omega_B/fg. The gas mass fractions depend on cosmology through the angular diameter distance and the r500 correction factors. For a flat universe (Omega_L = 1 - Omega_M) and h = 0.7, we find the measured gas mass fractions are consistent with Omega_M < 0.40, at 68% confidence. Including estimates of the baryons contained in galaxies and the baryons which failed to become bound during the cluster formation process, we find Omega_M ~ 0.25. |
