PLASMA INSTABILITIES IN THE CONTEXT OF CURRENT HELIUM SEDIMENTATION MODELS: DYNAMICAL IMPLICATIONS FOR THE ICM IN GALAXY CLUSTERS
PLASMA INSTABILITIES IN THE CONTEXT OF CURRENT HELIUM SEDIMENTATION MODELS: DYNAMICAL IMPLICATIONS FOR THE ICM IN GALAXY CLUSTERS
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当前氦沉降模型背景下的等离子体不稳定性：星系团中 ICM 的动力学含义
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
M. Pessah
中科院分区：
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作者：
Thomas Berlok;M. Pessah
了解氦是否可以沉积到星系团的核心对于宇宙学和天体物理学中的许多问题都很重要。目前解决这个问题的所有模型都是一维的，并且没有考虑到磁场可以有效地引导离子和电子，从而导致动量、热量和粒子扩散在弱碰撞群内介质（ICM）中的各向异性传输。这种各向异性可能导致各种各样的不稳定性，这可能与理解非均质介质的动力学相关。在本文中，我们考虑的径向温度和成分的配置文件，从一个国家的最先进的氦沉降模型，并分析其稳定性。我们发现，相关的径向配置文件是不稳定的不同种类的不稳定性，这取决于在所有半径的磁场取向。增长最快的模式通常与非均匀介质中的磁热不稳定性（MTI）和热流驱动的浮力不稳定性有关。我们发现，沉降的影响是增加（减少）预测的增长率在内部（外部）集群区域。与沉降时间尺度相比，不稳定模式增长迅速。这表明，从沉积模型中推断的成分梯度可能不是很可靠，因为沉积模型没有充分考虑到弱碰撞环境的各向异性特征。我们的研究结果强调了在理解ICM的气体动力学所涉及的微妙之处，并认为需要一个全面的方法来解决氦沉积超出目前的模型的问题。
Understanding whether Helium can sediment to the core of galaxy clusters is important for a number of problems in cosmology and astrophysics. All current models addressing this question are one-dimensional and do not account for the fact that magnetic fields can effectively channel ions and electrons, leading to anisotropic transport of momentum, heat, and particle diffusion in the weakly collisional intracluster medium (ICM). This anisotropy can lead to a wide variety of instabilities, which could be relevant for understanding the dynamics of heterogeneous media. In this paper, we consider the radial temperature and composition profiles as obtained from a state-of-the-art Helium sedimentation model and analyze its stability properties. We find that the associated radial profiles are unstable to different kinds of instabilities depending on the magnetic field orientation at all radii. The fastest growing modes are usually related to generalizations of the magnetothermal instability (MTI) and the heat-flux-driven buoyancy instability which operate in heterogeneous media. We find that the effect of sedimentation is to increase (decrease) the predicted growth rates in the inner (outer) cluster region. The unstable modes grow quickly compared to the sedimentation timescale. This suggests that the composition gradients as inferred from sedimentation models, which do not fully account for the anisotropic character of the weakly collisional environment, might not be very robust. Our results emphasize the subtleties involved in understanding the gas dynamics of the ICM and argue for the need of a comprehensive approach to address the issue of Helium sedimentation beyond current models.