【作者】 顾力意；

【导师】 徐海光；

【作者基本信息】 上海交通大学 ， 天体物理， 2010， 博士

【摘要】 在本论文中,利用新一代X射线天文卫星的高空间和高能量分辨能力,我们分析了星系团中央区域气体的二维温度结构特征和热力学成分,从而为解决星系团气体加热机制等重要前沿课题提供了观测约束。同时,进一步定量评估了探测到的二维温度结构以及其对应的气体加热对测量星系团总引力质量轮廓所造成的影响。(一)使用高质量Chandra观测数据,我们分析了红移为0.1左右的九个星系团中央400h7?11 kpc区域的二维气体温度分布。应用小波变换和傅里叶功率谱方法,我们探测到了尺度为100h?711 kpc左右的显著二维温度结构。这些二维温度结构的气体温度比周围气体温度高约2 ? 3 keV,所对应的能量超出为1058?60 erg。考虑到星系团气体中典型的湍流速度为200 ? 400 km s?1,这些二维温度结构的有效热传导时标约为108 ?109年,比气体冷却时间小一个量级。因此,可以排除非均匀辐射冷却造成这些温度结构的可能性。通过计算由中央AGN爆发所导致的气泡状结构上升时标,我们推测中央AGN反馈加热[1]有可能是形成这些二维温度结构的主要机制。为了进一步定量估计星系团中央区域的二维温度结构对总引力质量分布的X射线测量造成的偏离,我们分析了一个包含65个X射线亮星系团样本的二维温度分布和总引力质量轮廓。在流体静力学假定下,利用传统角向平均方法得到的星系团中央区域总引力质量轮廓显著偏离于扣除探测到的二维温度结构后的总引力质量轮廓,最大偏离为10?75%。这反映了目前利用X射线方法测量星系团中央区域暗物质分布的精度上限。同时这一工作也为将来精确计算星系团质量轮廓提供了条件。(二)为了更全面地研究星系团中央区域气体的热力学状态及其成分,我们分析了一个邻近的典型cD星系团A1795的高质量Chandra、XMM-Newton和Suzaku观测数据。我们发现在中央80h?711 kpc区域内主要存在两相星系团气体成分,其低温成分和高温成分的特征温度分别为2.0 ? 2.4 keV和5.0 ? 5.7 keV。同时,我们探测到了一个较弱的0.8 keV成分,对应中央cD星系内气体。通过对比二维辐射量度(emission measure)比值和金属丰度分布,我们发现在半径为50 ? 100h7?11kpc区域内低温成分含有较高的金属丰度。采用cD corona模型[2],我们解释了观测得到的两相气体温度、密度和辐射量度分布。在此模型中,因受到星系团磁场的约束气体低温成分分布于星系团中央区域,且与周围高温成分保持基本绝热。另外,由于此模型预言的加热源尺度和星系团中央射电瓣尺度一致(≈10h7?11kpc),我们推测中央星系AGN反馈能防止低温高密度成分过快冷却,使其保持热力学稳定态.更多还原

【Abstract】 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.更多还原