| In this dissertation, by analyzing the high quality data achieved from Chan-dra, XMM-Newton, and Suzaku satellites, we investigate the 2-D gas temperaturesubstructures and thermal conditions in the central regions of galaxy clusters,which pose constrains on the gas heating processes that dominates the thermalevolution history of intracluster medium (ICM). We further study the systematicbiases on the measurements of gravitating mass distributions induced by the 2-Dgas temperature substructures.(1) By analyzing the high quality Chandra data of nine intermediate-redshift(z≈0.1) galaxy clusters, we find that the single-phase ICM dominates the central400h?711 kpc regions. By calculating the 2-D gas temperature maps, we reveal theprevailing existence of temperature substructures on～100h?711 kpc scales in thecentral regions of nine intermediate-redshift (z≈0.1) galaxy clusters. Eachsubstructure contains a clump of hot plasma whose temperature is about 2 ? 3keV higher than the environment, corresponding to an excess thermal energyof～1058?60 erg per clump. Since if there were no significant non-gravitationalheating sources, these substructures would have perished in 108?9 yrs due tothermal conduction and turbulent ?ows, whose velocity is found to range fromabout 200 to 400 km s?1, we conclude that the substructures cannot be createdand sustained by inhomogeneous radiative cooling. By calculating the risingtime of AGN-induced buoyant bubbles, we speculate that the intermittent AGNoutbursts (≥1060 erg per burst), which result in buoyant bubbles that rise andheat the ICM simultaneously, may have played a crucial role in the forming ofthe high temperature substructures.In order to estimate the biases on X-ray measurements of gravitating mass distributions induced by the 2-D high temperature substructures in cluster's cen-tral region, we analyze the temperature maps and mass profiles of an extendedsample consisting of 65 galaxy clusters. We find that such temperature sub-structures can bias the azimuthally-averaged mass profiles by 10 ? 75%, whichsets an upper limit on the precision of current dark matter mass measurements.We propose that the temperature maps can be used to identify substructuresnot in hydrostatic equilibrium, and help improve the accuracies of X-ray massmeasurements.(3) Based on a detailed analysis of the high-quality Chandra, XMM-Newton,and Suzaku data of the X-ray bright cluster of galaxies Abell 1795, we report aclear preference for a two-phase ICM model, which consists of a cool (Tc≈2.0 ? 2.4 keV) and a hot (Th≈5.0 ? 5.7 keV) component that coexist anddominate the X-ray emission in the central 80h?711 kpc. A third weak emissioncomponent (T3≈0.8 keV) is also detected in the central region and is ascribedto the inter-stellar medium (ISM) of the cD galaxy. By analyzing the emissionmeasure ratio and gas metal abundance maps created from the Chandra data,we also detect a possible correlation between the spatial distributions of the coolphase gas and metal-rich gas in the 50 ? 100h7?11 kpc region. We employ the cDcorona model to explain the origin of the coexistence of the hot and cool phaseICM, by comparing model predictions with measured gas temperature, density,and emission measure distributions. In this model, we ascribe the cool phasecomponent to the gas constrained in the magnetic loops, which are surroundedby intruding hot ICM (i.e., the hot phase) and have been polluted by the metalssynthesized in the cD galaxy. And we find that AGN feedback energy released inthe innermost 10h7?11 kpc can serve as the heating source to prevent the cool phasegas from cooling down to temperatures much lower than the observed values.
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