Spiral Magnetohydrodynamic Density Waves with a Tangential Shear Force
Spiral Magnetohydrodynamic Density Waves with a Tangential Shear Force
复制标题
具有切向剪切力的螺旋磁流体动力密度波
DOI：
10.1086/320459
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
Z. Fan
中科院分区：
文献类型：
--
作者：
Y. Lou;C. Yuan;Z. Fan
螺旋星系的同步加速器射电连续辐射证明，螺旋星系的星际介质（ISM）中嵌入了估计强度为几微高斯或更强的磁场，并在大规模星系密度波螺旋结构中发挥重要的动力学和诊断作用，以及在磁场强度可能高于几十微高斯的中心区域形成紧密的环核螺旋。在本文中，我们研究了切向剪切力对带微分旋转的薄磁化气片中螺旋磁流体动力学（MHD）密度波的几种物理效应。这种切向剪切力在方位角方向上是惯性型的，主要由圆盘的微分旋转引起，仅对非轴对称MHD密度波摄动起作用。(1)短密度波、长密度波和开放密度波在接近重合时可能变得不稳定。(2)在林德布莱德共振之外，快速磁声密度波可能变得过稳定（振荡增长）。(3)低速MHD密度波在接近自转时可能变得不稳定。我们讨论了这些结果在多波长星系观测中的相关理论工作和概念应用，包括螺旋星系、棒旋星系和螺旋星系中心区域的紧环核螺旋。在角动量输运方面，由切向剪切力驱动的螺旋MHD密度波也应该在更广泛的天体物理背景下在磁化吸积盘中找到重要的应用。
Evidenced by synchrotron radio-continuum emissions from spiral galaxies, magnetic fields with estimated strengths of several microgauss or stronger are embedded in the interstellar medium (ISM) of spiral galaxies and play important dynamic and diagnostic roles in large-scale galactic density-wave spiral structures as well as in the formation of tight circumnuclear spirals in the central regions where magnetic field strengths may be higher than several tens of microgauss. In this paper, we examine several physical effects of the tangential shear force on spiral magnetohydrodynamic (MHD) density waves in a thin magnetized gas sheet with differential rotation. This tangential shear force in the azimuthal direction, mainly caused by the disk differential rotation, is of inertial type and operates only for nonaxisymmetric MHD density wave perturbations. We focus on shear-related processes of interest: (1) The short-, long-, and open-MHD density waves may become unstable near corotation. (2) Fast magnetoacoustic density waves may become overstable (oscillatory growth) outside the Lindblad resonances. (3) Slow MHD density waves may become unstable near corotation. We discuss relevant theoretical works and conceptual applications of these results to multiwavelength galactic observations, including spiral galaxies, barred spiral galaxies, and tight circumnuclear spirals in central regions of spiral galaxies. In terms of the angular momentum transport, spiral MHD density waves driven by the tangential shear force should also find important applications in magnetized accretion disks in broader astrophysical contexts.