X射线团簇形状对团簇物理的约束：局域X射线团簇与LCDM团簇的比较
Constraining Cluster Physics with the Shape of X-ray Clusters: Comparison of Local X-ray Clusters versus LCDM Clusters
摘要：
对团簇形成的模拟表明，在团簇形成过程中，重子向中心星系的凝聚可以使星系团中的气体分布形状明显变圆，即使半径大到维里半径的一半。然而，这样的模拟通常预测在星团维里半径内的恒星分数比从观测中推断的恒星质量大2到3倍。在这项工作中，我们比较椭圆率配置文件的集群模拟与重子冷却和没有集群椭圆率配置文件来自钱德拉和ROSAT观测，努力约束气体冷却和冷凝成星系团内的中央星系的分数。我们发现，所观察到的椭圆率分布是相当恒定的半径，平均椭圆率为0.18 +/- 0.05。所观察到的椭圆率分布与非辐射模拟的预测吻合得很好。另一方面，在包括辐射冷却、恒星形成和超新星反馈（但没有活动星系核反馈）的模拟中，星系团的椭圆率分布在所有半径上都明显偏离观测到的椭圆率分布。在星系团的内（外）区，冷却的模拟高估（低估）了椭圆率。通过比较有冷却和无冷却的模拟，我们表明，通过在模拟团簇的中心区域的冷却流的气体的冷却导致的气体分布在中心区域更扁圆，但使外部气体分布更球形。我们发现，晚时间的气体冷却和恒星的形成是负责显着扁圆的气体分布在集群核心，但集群核心以外的气体形状主要是由重子耗散在高红移z > 2。
英文摘要：
Simulations of cluster formation have demonstrated that condensation of baryons into central galaxies during cluster formation can drive the shape of the gas distribution in galaxy clusters significantly rounder, even at radii as large as half of the virial radius. However, such simulations generally predict stellar fractions within cluster virial radii that are ~2 to 3 times larger than the stellar masses deduced from observations. In this work we compare ellipticity profiles of clusters simulated with and without baryonic cooling to the cluster ellipticity profiles derived from Chandra and ROSAT observations in an effort to constrain the fraction of gas that cools and condenses into the central galaxies within clusters. We find that the observed ellipticity profiles are fairly constant with radius, with an average ellipticity of 0.18 +/- 0.05. The observed ellipticity profiles are in good agreement with the predictions of non-radiative simulations. On the other hand, the ellipticity profiles of the clusters in simulations that include radiative cooling, star formation, and supernova feedback (but no AGN feedback) deviate significantly from the observed ellipticity profiles at all radii. The simulations with cooling overpredict (underpredict) ellipticity in the inner (outer) regions of galaxy clusters. By comparing the simulations with and without cooling, we show that the cooling of gas via cooling flows in the central regions of simulated clusters causes the gas distribution to be more oblate in the central regions, but makes the outer gas distribution more spherical. We find that late-time gas cooling and star formation are responsible for the significantly oblate gas distributions in cluster cores, but the gas shapes outside of cluster cores are set primarily by baryon dissipation at high redshift z > 2.
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