团内介质的大尺度不均匀性：利用观测到的方位角散射改进质量估算
Large-scale inhomogeneities of the intracluster medium: improving mass estimates using the observed azimuthal scatter
摘要：
使用一组流体动力学模拟的62个星系团和团体，我们研究的ICM的不均匀性，集中在大尺度上，不像团块，是最难识别的。为此，我们引入了剩余块度的概念，CR，它量化了ICM的大尺度不均匀性。在表明这个量可以鲁棒地定义为放松系统，我们描述了它如何随半径，质量和动态状态的晕。最重要的是，我们观察到，它引入了一个高估的密度分布的确定从X射线发射，这转化为一个系统的高估6（12）%的测量M_气体在R_200为我们的放松（扰动）集群样本。与此同时，C_R随半径的增加也导致流体静力平衡质量（M_he）的测量系统性低估了~2%，这增加了之前的测量结果，导致f_气体系统性高估了~8.5%在我们的放松样本中。由于ICM的残留结块是不能直接观察到的，我们研究了它的相关性与方位角散射的X射线表面亮度的晕和y参数配置文件。我们发现它们的相关性是非常显著的（r_S = 0.6-0.7），允许定义在X射线表面亮度轮廓和y参数中测量的方位角散射作为C_R的鲁棒代理。在给出一个连接这两个量的函数后，我们得到，用方位角散射校正观测到的气体密度分布，消除了弛豫物体M_gas测量中的偏差，在2R_200以下为（0+/-2）%，而在扰动物体M_gas测量中偏差减小了3倍。该方法还允许消除测量M_he和f_gas的系统性，尽管仍然存在显著的晕到晕散射。（节略）
英文摘要：
Using a set of hydrodynamical simulations of 62 galaxy clusters and groups we study the ICM of inhomogeneities, focusing on the ones on the large scale that, unlike clumps, are the most difficult to identify. To this purpose we introduce the concept of residual clumpiness, C_R, that quantifies the large-scale inhomogeneity of the ICM. After showing that this quantity can be robustly defined for relaxed systems, we characterize how it varies with radius, mass and dynamical state of the halo. Most importantly, we observe that it introduces an overestimate in the determination of the density profile from the X-ray emission, which translates into a systematic overestimate of 6 (12)% in the measurement of M_gas at R_200 for our relaxed (perturbed) cluster sample. At the same time, the increase of C_R with radius introduces also a ~2% systematic underestimate in the measurement of the hydrostatic-equilibrium mass (M_he), which adds to the previous one generating a systematic ~8.5% overestimate in f_gas in our relaxed sample. Since the residual clumpiness of the ICM is not directly observable, we study its correlation with the azimuthal scatter in the X-ray surface brightness of the halo and in the y-parameter profiles. We find that their correlation is highly significant (r_S = 0.6-0.7), allowing to define the azimuthal scatter measured in the X-ray surface brightness profile and in the y-parameter as robust proxies of C_R. After providing a function that connects the two quantities, we obtain that correcting the observed gas density profiles using the azimuthal scatter eliminates the bias in the measurement of M_gas for relaxed objects, which becomes (0+/-2)% up to 2R_200, and reduces it by a factor of 3 for perturbed ones. This method allows also to eliminate the systematics on the measurements of M_he and f_gas, although a significant halo to halo scatter remains. (abridged)
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