论文标题
低$β$磁盘中的多相环气：湍流和磁场逆转
Multiphase Circumnuclear Gas in a Low-$β$ Disk: Turbulence and Magnetic Field Reversals
论文作者
论文摘要
我们使用全局3D磁性水力学（MHD）仿真研究了磁场化的多相气体的磁场结构和动力学。我们考虑了由于活性银河核（AGN）引起的辐射冷却和X射线加热的影响。气盘由带有（1）冷（$ \ leq 10^3 $ k）和薄的多相气体组成，以及（2）温暖（$ \ sim 10^4 $ k）和较厚的成分，具有广泛的数量密度。最大的湍流磁能与湍流运动中的热和湍流动能相当。我们证实，环境冷气中温暖气体的湍流速度是由磁对感染的不稳定引起的。由于磁盘不稳定（MRI）引起的湍流磁场是在磁盘中开发的，但是平均环形磁场在准稳态状态下占主导和支撑，那里的等离子体 - $β$，气体压力与磁压之间的比率很低（$β<1 $）。正如在旋转磁盘的绝热MHD模拟中经常看到的那样，平均环形场的方向也会随时间定期逆转，即使在多相气体结构中。方向逆转是由磁通量从磁盘垂直逃脱的，以及MRI和Parker不稳定性的组合引起的。
We studied the magnetic field structures and dynamics of magnetized multiphase gas on parsec scales around supermassive black holes by using global 3D magnetohydrodynamics (MHD) simulations. We considered the effect of radiative cooling and X-ray heating due to active galactic nuclei (AGNs). The gas disk consists of a multiphase gas with (1) cold ($\leq 10^3$ K) and thin, and (2) warm ($\sim 10^4$ K) and thick components with a wide range of number densities. The turbulent magnetic energy at maximum is comparable to the thermal and turbulent kinetic energies in the turbulent motion. We confirmed that the turbulent velocity of the warm gas in the ambient cold gas is caused by magnetoconvective instability. The turbulent magnetic field due to magnetorotational instability (MRI) is developed in the disk, but the mean toroidal magnetic field dominates and supports in a quasi-steady state, where the plasma-$β$, the ratio between gas pressure and magnetic pressure, is low ($β< 1$). As often seen in adiabatic MHD simulations of rotating disks, the direction of the mean toroidal field periodically reverses with time even in multiphase gas structures. The direction reversal is caused by magnetic flux vertically escaping from the disk and by the combination of the MRI and the Parker instability.
