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arXiv 1003.2270astro-ph.CO
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Lambda-CDM团簇中气体、引力势和暗物质的相互作用

Shapes of Gas, Gravitational Potential and Dark Matter in Lambda-CDM Clusters

Erwin T. Lau, Daisuke Nagai, Andrey V. Kravtsov, Andrew R. Zentner

备注：
11 pages, 8 figures, 3 tables, updated to match the version accepted for publication in the Astrophysical Journal
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摘要：

我们提出了分析的三维形状的星团内的气体在宇宙学模拟中形成的Lambda CDM宇宙学和比较它的形状的暗物质分布和形状的整体等势面。我们发现，在模拟辐射冷却，恒星形成和恒星反馈（CSF），星团核心外的气体是更球形相比，非辐射（NR）模拟，而在核心的气体在CSF运行是更三轴，并具有明显的扁圆形。后者反映了气体的持续冷却，当它失去热能时，它会沉降成一个厚的扁椭圆体。因此，团簇内部区域的气体形状可以是气体冷却的有用诊断。我们发现，气体跟踪的形状的潜在的核心以外，而预期的流体静力平衡。然而，在较小的半径，气体和潜在的形状显着不同。在CSF运行中，差异反映了气体部分旋转支撑的事实。有趣的是，我们发现，在NR模拟气体和潜在的形状之间的差异，在小半径是由于随机气体运动，这使得气体分布比等势面更球形。最后，我们使用模拟钱德拉X射线地图表明，在三维气体分布中观察到的形状差异是可辨别的椭圆度的X射线等照度线。因此，将模拟星团中测得的椭圆度与观测结果进行对比，可以限制星团内介质的冷却量和星团核心中随机气体运动的存在。

英文摘要：

We present analysis of the three-dimensional shape of intracluster gas in clusters formed in cosmological simulations of the Lambda-CDM cosmology and compare it to the shape of dark matter distribution and the shape of the overall isopotential surfaces. We find that in simulations with radiative cooling, star formation and stellar feedback (CSF), intracluster gas outside the cluster core is more spherical compared to non-radiative (NR) simulations, while in the core the gas in the CSF runs is more triaxial and has a distinctly oblate shape. The latter reflects the ongoing cooling of gas, which settles into a thick oblate ellipsoid as it loses thermal energy. The shape of the gas in the inner regions of clusters can therefore be a useful diagnostic of gas cooling. We find that gas traces the shape of the underlying potential rather well outside the core, as expected in hydrostatic equilibrium. At smaller radii, however, the gas and potential shapes differ significantly. In the CSF runs, the difference reflects the fact that gas is partly rotationally supported. Interestingly, we find that in NR simulations the difference between gas and potential shape at small radii is due to random gas motions, which make the gas distribution more spherical than the equipotential surfaces. Finally, we use mock Chandra X-ray maps to show that the differences in shapes observed in three-dimensional distribution of gas are discernible in the ellipticity of X-ray isophotes. Contrasting the ellipticities measured in simulated clusters against observations can therefore constrain the amount of cooling of the intracluster medium and the presence of random gas motions in cluster cores.

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