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arXiv 1504.08065astro-ph.GAastro-ph.HEastro-ph.SR
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银河系隆起区磁活动驱动的随机非圆运动和外流

Stochastic Noncircular Motion and Outflows Driven by Magnetic Activity in the Galactic Bulge Region

Takeru K. Suzuki, Yasuo Fukui, Kazufumi Torii, Mami Machida, Ryoji Matsumoto

摘要:

通过对具有轴对称引力势的银河系进行全球磁流体动力学模拟,我们提出空间依赖的磁场放大可能解释了银河系中心区域气体的非圆形运动。在核球区,旋转频率的径向分布一般不是单调的。磁场的放大在具有较强的差旋转的区域中增强,因为磁旋转不稳定性和场线拉伸更有效。放大的磁场的强度达到>~ 0.5 mG,并且气体的径向流动由通过湍流磁场的角动量的不均匀传输激发,该湍流磁场以空间依赖的方式放大。此外,磁压力梯度力也以类似的方式驱动径向流。结果表明,由于磁湍流的不稳定性,模拟的位置-速度图呈现出随时间变化的不对称平行四边形形状;该模型为平行四边形形状的中心分子区提供了一种替代棒势驱动模型的可行方法.这是一个自然的延伸到中心的几个100 pc的磁活动,这是观察到的分子环半径从几个100 pc到1 kpc。此外,时间平均的净气体流量是向外的,而流量是高度依赖于时间的,我们讨论的流出从隆起的观点。

英文摘要:

By performing a global magneto-hydrodynamical simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic center region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches >~ 0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. In addition, the magnetic pressure-gradient force also drives radial flows in a similar manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram-shape of the central molecular zone. This is a natural extension into the central few 100 pc of the magnetic activity, which is observed as molecular loops at radii from a few 100 pc to 1 kpc. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time-dependent, which we discuss from a viewpoint of the outflow from the bulge.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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