2000ApJ...540..614M

We define a 90% complete, volume-limited sample of 31 z<0.1 X-ray clusters and present a systematic analysis of public ROSAT PSPC data on 22 of these objects. Our efforts are undertaken in support of the Penn/OVRO Sunyaev-Zeldovich Effect (SZE) survey, and to this end we present predictions for the inverse Compton optical depth toward all 22 of these clusters. We have performed detailed Monte Carlo simulations in order to understand the effects of the cluster profile uncertainties on the SZE predictions given the OVRO 5.5 m telescope beam and switching patterns. We also present a similar analysis for the upcoming ACBAR experiment. For most of the clusters in the sample, we find less than a 5% uncertainty in the SZE predictions due to an imperfect knowledge of the profile. A comparison of different cooling-flow modeling strategies shows that our results are robust in this respect. The profile uncertainties are then one of the least significant components of our error budget for SZE-based distance measurements. The density models that result from this analysis also yield baryonic masses and, under the assumption of hydrostatic equilibrium, total masses and baryon mass fractions. Our Monte Carlo profile analysis indicates that the baryon masses within 1 h^–1₁₀₀ Mpc for these clusters are accurate to better than ∼5% and unaffected by realistic PSPC systematics. In the sample as a whole, we find a mean gas mass fraction of (7.02±0.28)h^–3/2₁₀₀x10^–2 internal to R₅₀₀∼1 h^–1₁₀₀ Mpc. This is in agreement with previous X-ray cluster analyses, which indicate an overabundance of baryons relative to the prediction of big bang nucleosynthesis for an Ω_M=1 universe. Our analysis of the X-ray spectra confirms a previous claim of an excess absorbing column density toward A478, but we do not find evidence for anomalous column densities in the other 21 clusters. We also find some indications of an excess of soft counts in the ROSAT PSPC data. A measurement of H₀ using these models and OVRO SZE determinations will be presented in a second paper.