1999ApJ...523L.137D

We constrain Ω_m through a maximum likelihood analysis of temperatures and redshifts of the high-redshift clusters from the Extended Medium-Sensitivity Survey (EMSS). We simultaneously fit the low-redshift Markevitch sample (an all-sky sample from ROSAT with z=0.04-0.09), a moderate redshift EMSS sample from Henry (nine clusters with z=0.3-0.4), and a more distant EMSS sample (five clusters with z=0.5-0.83 from Donahue et al.) finding best-fit values of Ω_m=0.45±0.1 for an open universe and Ω_m=0.27±0.1 for a flat universe. We individually analyze the effects of our governing assumptions, including the evolution and dispersion of the cluster luminosity-temperature relation, the evolution and dispersion of the cluster mass-temperature relation, the choice of low-redshift cluster sample, and the accuracy of the standard Press-Schechter formalism. We examine whether the existence of the massive distant cluster MS 1054-0321 skews our results, and we find its effect to be small. From our maximum likelihood analysis we conclude that our results are not very sensitive to our assumptions, and bootstrap analysis shows that our results are not sensitive to the current temperature measurement uncertainties. The systematic uncertainties are ~±0.1, and Ω_m=1 universes are ruled out at greater than 99.7% (3 σ) confidence.