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arXiv 1409.6300astro-ph.GAastro-ph.CO
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作为ICM物理探测器的剥离椭圆星系:I.剥离椭圆星系内和周围的尾流、尾流和流型

Stripped elliptical galaxies as probes of ICM physics: I. Tails, wakes, and flow patterns in and around stripped ellipticals

E. Roediger, R. P. Kraft, P. E. J. Nulsen, W. R. Forman, M. Machacek, S. Randall, C. Jones, E. Churazov, R. Kokotanekova

摘要:

椭圆星系团由于在星系团内介质(ICM)中的运动而逐渐被剥夺了大气层。深X射线观测揭示了星系残余大气层的精细结构及其气体尾部和尾流。这种精细结构取决于动力学条件(星系势、初始气体含量、穿过主星系团的轨道)、轨道阶段(早期坠落、近心通过前/后)和ICM等离子体特性(热导率、粘度、磁场结构)。我们的目标是解开动力学和等离子体的影响,以使用剥离椭圆作为ICM等离子体性质的探针。这是一个系列的第一篇论文研究的流体动力学渐进气提通过无粘流体动力学模拟。我们区分了一个持久的初始松弛阶段和一个准稳定的剥离阶段。在准定常剥离,ICM流周围的残余大气类似于固体周围的流动,包括一个“死水”区在近尾流。气体主要通过开尔文-亥姆霍兹不稳定性从残余大气的侧面剥离。下游的大气在很大程度上受到ICM风的屏蔽,因此形成了一个尾巴。从观测上看,这两个“残余尾巴”和尾流中的剥离气体都可以作为“尾巴”出现,但只有在尾流中,星系气体才能与周围的ICM混合。虽然定性结果是通用的,但这里提供的模拟是针对室女座椭圆星系M89(NGC 4552)的,以便与观测进行最直接的比较。本系列的第二和第三篇论文描述了粘性的影响,并分别与钱德拉和XMM-牛顿观测进行了比较。

英文摘要:

Elliptical cluster galaxies are progressively stripped of their atmospheres due to their motion through the intra-cluster medium (ICM). Deep X-ray observations reveal the fine-structure of the galaxy's remnant atmosphere and its gas tail and wake. This fine-structure depends on dynamic conditions (galaxy potential, initial gas contents, orbit through the host cluster), orbital stage (early infall, pre-/post-pericenter passage), and ICM plasma properties (thermal conductivity, viscosity, magnetic field structure). We aim to disentangle dynamic and plasma effects in order to use stripped ellipticals as probes of ICM plasma properties. This first paper of a series investigates the hydrodynamics of progressive gas stripping by means of inviscid hydrodynamical simulations. We distinguish a long-lasting initial relaxation phase and a quasi-steady stripping phase. During quasi-steady stripping, the ICM flow around the remnant atmosphere resembles the flow around solid bodies, including a `deadwater' region in the near wake. Gas is stripped from the remnant atmosphere predominantly at its sides via Kelvin-Helmholtz instabilities. The downstream atmosphere is largely shielded from the ICM wind and thus shaped into a tail. Observationally, both, this `remnant tail' and the stripped gas in the wake can appear as a `tail', but only in the wake can galactic gas mix with the ambient ICM. While the qualitative results are generic, the simulations presented here are tailored to the Virgo elliptical galaxy M89 (NGC 4552) for the most direct comparison to observations. Papers II and III of this series describe the effect of viscosity and compare to Chandra and XMM-Newton observations, respectively.

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