Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky
Deep Chandra observation and numerical studies of the nearest cluster cold front in the sky
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天空中最近星团冷锋的深钱德拉观测和数值研究
DOI：
10.1093/mnras/stv2358
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发表时间：
2016
影响因子：
4.8
通讯作者：
J. S. Sanders
中科院分区：
文献类型：
--
作者：
N. Werner;J. A. ZuHone;I. Zhuravleva;Y. Ichinohe;A. Simionescu;S. W. Allen;M. Markevitch;A. C. Fabian;U. Keshet;E. Roediger;M. Ruszkowski;J. S. Sanders
我们提出了一个非常深（500千秒）Chandra观测的结果，沿着与定制的数值模拟，最近的，最好的解决集群冷锋在天空中，这是90千秒差距（19弧分）的西北部的M 87。锋面的北方部分看起来最尖锐，宽度小于2.5千秒差距（1.5库仑平均自由路径;置信度为99%）。沿锋面沿着各处，温度不连续性小于4-8 kpc，金属度梯度小于6 kpc，表明扩散、传导和混合在界面上受到抑制。这种传输过程可以被与冷锋对齐的磁场自然地抑制。有趣的是，磁流体动力学模拟的比较表明，为了保持所观察到的尖锐的密度和温度的不连续性，传导也必须被抑制沿着磁场线。然而，冷锋的西北部被观察到有一个非零的宽度。虽然其他的解释是可能的，扩大是与存在的开尔文-亥姆霍兹不稳定性（KHI）的长度尺度上的几个千秒差距一致。基于与模拟的比较，KHI的存在将意味着有效的粘度的集群内介质被抑制了一个以上的数量级相对于各向同性斯皮策的温度依赖性粘度。在冷锋下，我们观察到比周围气体亮10%的准线性特征，并且在投影中彼此分离15 kpc。与定制的数值模拟的比较表明，所观察到的现象可能是由于冷锋下方宽层中的气体晃动放大了磁场，其中磁压达到热压力的0.5%-10%，降低了明亮特征之间的气体密度。
We present the results of a very deep (500 ks)Chandraobservation, along with tailored numerical simulations, of the nearest, best resolved cluster cold front in the sky, which lies 90 kpc (19 arcmin) to the north-west of M 87. The northern part of the front appears the sharpest, with a width smaller than 2.5 kpc (1.5 Coulomb mean free paths; at 99 per cent confidence). Everywhere along the front, the temperature discontinuity is narrower than 4–8 kpc and the metallicity gradient is narrower than 6 kpc, indicating that diffusion, conduction and mixing are suppressed across the interface. Such transport processes can be naturally suppressed by magnetic fields aligned with the cold front. Interestingly, comparison to magnetohydrodynamic simulations indicates that in order to maintain the observed sharp density and temperature discontinuities, conduction must also be suppressed along the magnetic field lines. However, the northwestern part of the cold front is observed to have a non-zero width. While other explanations are possible, the broadening is consistent with the presence of Kelvin–Helmholtz instabilities (KHI) on length-scales of a few kpc. Based on comparison with simulations, the presence of KHI would imply that the effective viscosity of the intracluster medium is suppressed by more than an order of magnitude with respect to the isotropicSpitzer-like temperature dependent viscosity. Underneath the cold front, we observe quasi-linear features that are ∼10 per cent brighter than the surrounding gas and are separated by ∼15 kpc from each other in projection. Comparison to tailored numerical simulations suggests that the observed phenomena may be due to the amplification of magnetic fields by gas sloshing in wide layers below the cold front, where the magnetic pressure reaches ∼5–10 per cent of the thermal pressure, reducing the gas density between the bright features.
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DOI：
10.1086/425952
发表时间：
2004
期刊：
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影响因子：
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