``Galaxy Cluster Gas Mass Fractions from SunyaevZel'dovich Effect
Measurements: Constraints on Omega_M''

Abstract
Using sensitive centimeterwave receivers mounted on the Owens Valley
Radio Observatory and BerkeleyIllinoisMarylandAssociation
millimeter arrays, we have obtained interferometric measurements of
the SunyaevZeldovich (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 Xray 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.

