Four Measures of the Intracluster Medium Temperature and Their Relation to a Cluster’s Dynamical State
Four Measures of the Intracluster Medium Temperature and Their Relation to a Cluster’s Dynamical State
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DOI：
10.1086/318249
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发表时间：
2000-04
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影响因子：
--
通讯作者：
B. Mathiesen;A. Evrard
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文献类型：
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作者：
B. Mathiesen;A. Evrard
我们采用了24个流体动力集群模拟的集合来创建质量与钱德拉预期性能相当的空间和光谱分辨率图像。假设太阳金属丰度为0.3，用XSPEC“MEKAL”程序表示模拟质量元的发射，所得光谱拟合为单一温度模型。尽管在星团气体中有明显的偏离等温，但单温度模型对20,000源光子光谱的拟合是可以接受的。光谱拟合温度Ts通常低于质量加权平均温度Tm，这是由于在分层聚类过程中被吸积的较冷气体的软线发射的影响。这种偏差的性质取决于用于光谱拟合的带通。在0.5 ~ 9.5 keV的类钱德拉带通中，我们发现分数偏差几乎一致地为(Tm - Ts)/Ts≃20%，尽管较小的簇有时会表现出更大的偏差。然而，如果将最小能量阈值提高到2 keV，则线发射对光谱的影响大大降低，对于较小的簇，Ts几乎成为Tm的无偏估计量。在该带通中，Ts相对于Tm的分数偏差与尺度有关，并遵循近似关系(Tm - Ts)/Ts = 0.2 log10 Tm。这使得模拟的观测到的MICM- ts关系斜率约为1.6，介于虚拟关系M∝T和观测关系MICM∝T2之间。我们在星系团演化历史的16个时期对每个星系团进行了跟踪，并对质量比超过10%的合并事件进行了编目，以研究光谱温度与主要合并事件的接近程度之间的关系。相对于平均质量-温度关系来说非常冷的星团优先靠近主要的合并，这表明一种可行的观测方法可以从总体中剔除动态年轻星团的子集。
We employ an ensemble of 24 hydrodynamic cluster simulations to create spatially and spectrally resolved images of quality comparable to Chandra's expected performance. Emission from simulation mass elements is represented using the XSPEC "MEKAL" program assuming 0.3 solar metallicity and the resulting spectra are fitted with a single-temperature model. Despite significant departures from isothermality in the cluster gas, single-temperature models produce acceptable fits to 20,000 source photon spectra. The spectral fit temperature Ts is generally lower than the mass-weighted average temperature Tm due to the influence of soft line emission from cooler gas being accreted as part of the hierarchical clustering process. The nature of this deviation depends on the bandpass used for spectral fitting. In a Chandra-like bandpass of 0.5 to 9.5 keV we find a nearly uniform fractional bias of (Tm - Ts)/Ts ≃ 20%, although smaller clusters sometimes demonstrate much greater deviations. If the minimum energy threshold is raised to 2 keV, however, the effect of line emission on the spectrum is greatly decreased and Ts becomes a nearly unbiased estimator of Tm for smaller clusters. The fractional deviation in Ts relative to Tm is scale-dependent in this bandpass and follows the approximate relation (Tm - Ts)/Ts = 0.2 log10 Tm. This results in an observed MICM-Ts relationship for the simulations with slope of about 1.6, intermediate between the virial relation M ∝ T and the observed relation MICM ∝ T2. Tracking each cluster in the ensemble at 16 epochs in its evolutionary history, we catalog merger events with mass ratios exceeding 10% in order to investigate the relationship between spectral temperature and proximity to a major merger event. Clusters that are very cool relative to the mean mass-temperature relationship lie preferentially close to a major merger, suggesting a viable observational method to cull a subset of dynamically young clusters from the general population.