论文标题
两相星际介质中的湍流元量
Turbulent dynamo in the two-phase interstellar medium
论文作者
论文摘要
磁场是恒星形成星系的湍流星际介质（ISM）的动态重要组成部分。这些磁场是由于发电机动作引起的，这是将湍流动能转换为磁能的过程。比湍流驾驶尺度低的发电机称为湍流发电机。 ISM是一种多相培养基，观察结果表明磁场的性能与相位不同。在这里，我们旨在研究湍流发电机的性质如何取决于阶段。我们在两相培养基中模拟非等温湍流发电机（大多数以前的工作假设是等温气体）。我们表明，温暖阶段（$ t \ ge10^3〜 {\ rm k} $）是跨性别者，冷阶段（$ t <10^3〜 {\ rm k} $）是超音速的。我们发现，在两个阶段，在成倍增长阶段的磁场的生长速率相似。我们计算了负责扩增和破坏涡度的术语，并表明在两个阶段，由于湍流运动而放大了涡度，在温暖阶段被斜压项进一步扩大，并在冷阶段存在对数密度梯度的情况下被粘性相互作用的术语破坏。我们发现，由于较强的洛伦兹力，在冷相中，磁与湍流动能的最终比率较低。我们表明，非等温湍流发电机与其等温对应物有显着差异，这表明需要研究多相培养基中的湍流发电机。
Magnetic fields are a dynamically important component of the turbulent interstellar medium (ISM) of star-forming galaxies. These magnetic fields are due to a dynamo action, which is a process of converting turbulent kinetic energy to magnetic energy. A dynamo that acts at scales less than the turbulent driving scale is known as the turbulent dynamo. The ISM is a multiphase medium and observations suggest that the properties of magnetic fields differ with the phase. Here, we aim to study how the properties of the turbulent dynamo depend on the phase. We simulate the non-isothermal turbulent dynamo in a two-phase medium (most previous work assumes an isothermal gas). We show that the warm phase ($T\ge10^3~{\rm K}$) is transsonic and the cold phase ($T<10^3~{\rm K}$) is supersonic. We find that the growth rate of magnetic fields in the exponentially growing stage is similar in both phases. We compute the terms responsible for amplification and destruction of vorticity and show that in both phases vorticity is amplified due to turbulent motions, further amplified by the baroclinic term in the warm phase, and destroyed by the term for viscous interactions in the presence of logarithmic density gradients in the cold phase. We find that the final ratio of magnetic to turbulent kinetic energy is lower in the cold phase due to a stronger Lorentz force. We show that the non-isothermal turbulent dynamo is significantly different from its isothermal counterpart and this demonstrates the need for studying the turbulent dynamo in a multiphase medium.
