从X射线表面亮度提取星系团气体不均匀性：一种统计方法及其对Abell 3667的应用
Extracting Galaxy Cluster Gas Inhomogeneity from X-ray Surface Brightness: A Statistical Approach and Application to Abell 3667
摘要：
我们以前的分析表明，小尺度的波动在集群内介质（ICM）从宇宙学流体动力学模拟遵循对数正态分布。为了检验ICM的对数正态性质直接对星系团的X射线观测，我们开发了一种方法，提取的三维特性的波动从二维X射线表面亮度的统计信息。我们首先创建一组具有对数正态波动的合成簇。对这些人工合成的团簇进行模拟观测，我们发现所得到的X射线表面亮度波动也很好地遵循对数正态分布。对合成团簇的系统分析提供了密度涨落与X射线表面亮度之间的经验关系。分析了星系团Abell 3667的\chandra观测结果，发现其X射线表面亮度起伏服从对数正态分布。虽然对数正态模型最初是由宇宙学流体动力学模拟激发的，但这是第一次在真实星系团中观测到对数正态特征。最后，我们检查的集群从宇宙流体动力学模拟的合成集群的结果。由于模拟团簇所表现出的复杂结构，经验关系表现出较大的离散性。然而，我们能够再现真实值的波动幅度的模拟集群内的两个因素，从他们的X射线表面亮度单独。结合现有的观测数据，我们的方法在描述和推断星系团三维不均匀性的统计特性方面是有用的。
英文摘要：
Our previous analysis indicates that small-scale fluctuations in the intracluster medium (ICM) from cosmological hydrodynamic simulations follow the lognormal distribution. In order to test the lognormal nature of the ICM directly against X-ray observations of galaxy clusters, we develop a method of extracting statistical information about the three-dimensional properties of the fluctuations from the two-dimensional X-ray surface brightness. We first create a set of synthetic clusters with lognormal fluctuations. Performing mock observations of these synthetic clusters, we find that the resulting X-ray surface brightness fluctuations also follow the lognormal distribution fairly well. Systematic analysis of the synthetic clusters provides an empirical relation between the density fluctuations and the X-ray surface brightness. We analyze \chandra observations of the galaxy cluster Abell 3667, and find that its X-ray surface brightness fluctuations follow the lognormal distribution. While the lognormal model was originally motivated by cosmological hydrodynamic simulations, this is the first observational confirmation of the lognormal signature in a real cluster. Finally we check the synthetic cluster results against clusters from cosmological hydrodynamic simulations. As a result of the complex structure exhibited by simulated clusters, the empirical relation shows large scatter. Nevertheless we are able to reproduce the true value of the fluctuation amplitude of simulated clusters within a factor of two from their X-ray surface brightness alone. Our current methodology combined with existing observational data is useful in describing and inferring the statistical properties of the three dimensional inhomogeneity in galaxy clusters.
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