TWO-FLUID MHD SIMULATIONS OF CONVERGING HI FLOWS IN THE INTERSTELLAR MEDIUM. I: METHODOLOGY AND BASIC RESULTS
TWO-FLUID MHD SIMULATIONS OF CONVERGING HI FLOWS IN THE INTERSTELLAR MEDIUM. I: METHODOLOGY AND BASIC RESULTS
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发表时间：
2019
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通讯作者：
T. Inoue;S. Inutsuka
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作者：
T. Inoue;S. Inutsuka
本文发展了一种求解两种流体（摩擦力/加热、电离和复合）耦合的无条件稳定的数值方法，并利用二维两流体磁流体动力学模拟方法研究了恒星介质中弱电离和磁化的激波提供的热不稳定气体的动态凝聚过程。如果忽略磁场的影响，由热不稳定性引起的凝结可以产生高密度云，其物理条件与分子云（分子云的前身）相对应。本文研究了磁场对超声速会聚HI流演化的影响，着重研究了磁场与会聚流方向正交的情况。我们发现，平行于流动的磁压梯度阻止了高密度和高柱密度云的形成，而是产生了碎片化的、非连续的HI云。与没有磁场的情况相比，在这种受限的几何形状下，磁场急剧减少了直接从温暖的中性介质中快速形成分子云的机会。
We develop an unconditionally stable numerical method for s olving the coupling between two fluids (frictional forces/heatings, ionizatio n, and recombination), and investigate the dynamical condensation process of thermally unstable gas that is provided by the shock waves in a weakly ionized and magnetized in t rstellar medium by using two-dimensional two-fluid magnetohydrodynamical si mulations. If we neglect the effect of magnetic field, it is known that condensation dr iven by thermal instability can generate high density clouds whose physical condition c orresponds to molecular clouds (precursor of molecular clouds). In this paper, we st udy the effect of magnetic field on the evolution of supersonic converging HI flows and focus on the case in which the orientation of magnetic field to converging flows is orthogonal. We show that the magnetic pressure gradient parallel to the flows pre vents the formation of high density and high column density clouds, but instead generat es fragmented, filamentary HI clouds. With this restricted geometry, magnetic field dra stically diminishes the opportunity of fast molecular cloud formation directly from t he warm neutral medium, in contrast to the case without magnetic field.