Four Measures of the Intracluster Medium Temperature and Their Relation to a Cluster’s Dynamical State

We employ an ensemble of hydrodynamic cluster simulations to create spatiallyand spectrally resolved images of quality comparable to Chandra's expectedperformance. Emission from simulation mass elements is represented using theXSPEC mekal program assuming 0.3 solar metallicity, and the resulting spectraare fit with a single-temperature model. Despite significant departures fromisothermality in the cluster gas, single-temperature models produce acceptablefits to 20,000 source photon spectra. The spectral fit temperature T_s isgenerally lower than the mass weighted average temperature T_m due to theinfluence of soft line emission from cooler gas being accreted as part of thehierarchical clustering process. In a Chandra-like bandpass of 0.5 to 9.5 keVwe find a nearly uniform fractional bias of (T_m-T_s)/T_s = 20% with occasionallarge deviations in smaller clusters. In the more traditional 2.0 to 9.5 keVbandpass, the fractional deviation is scale-dependent and on average followsthe relation (T_m-T_s)/T_s = 0.2 log(T_m). This bias results in a spectralmass-temperature relationship with slope about 1.6, intermediate between thevirial relation M ~ T_m^{3/2} and the observed relation M_{ICM} ~ T^2. Imagingeach cluster in the ensemble at 16 epochs in its evolutionary history, wecatalogue merger events with mass ratios exceeding 10% in order to investigatethe relationship between spectral temperature and proximity to a major mergerevent. Clusters that are very cool relative to the mean mass-temperaturerelationship lie preferentially close to a merger, suggesting a viableobservational method to cull a subset of dynamically young clusters from thegeneral population.