X-ray Temperatures for the EMSS High Redshift Cluster Sample:   Constraints on Cosmology and the Dark Energy Equation of State
  We measure the X-ray temperature (and luminosity) with ASCA of all but one cluster in the Einstein Extended Medium Sensitivity Survey (EMSS) high redshift (z > 0.3) sample. We compare these data to a complete sample of low redshift clusters that also has temperature measurements, thereby providing cosmological constraints. We incorporate many improvements over our previous work. We find an allowed band in the Omega_{m0} - Omega_{Lambda0} plane of different orientation to the band of constraints provided by the supernovae Ia Hubble diagram and the cosmic microwave background fluctuations. All three bands intersect at the same place: Omega_{m0} ~ 0.3, Omega_{Lambda0} ~ 0.7. We measure the quintessence equation of state parameter to be w = -(0.42 pm 0.21) (68% confidence for 1 interesting parameter), consistent with previously determined upper limits. We measure the normalization of the mass fluctuation power spectrum to be sigms_8 = 0.66 pm 0.16 (68% confidence for 3 interesting parameters). Systematic errors are larger than the statistical errors only for sigma_8 with our sample, thus the errors for it depends on the details of the marginalization over the temperature - mass normalization. 
J. Patrick Henry