Galactic spiral patterns and dynamo action – II. Asymptotic solutions
Galactic spiral patterns and dynamo action – II. Asymptotic solutions
复制标题
银河螺旋模式和发电机作用 – II。
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
A. Shukurov
中科院分区：
文献类型：
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作者：
L. Chamandy;K. Subramanian;A. Shukurov
Chamandy et al.（2013，以下简称Paper I）通过数值模拟开始了对受星系螺旋图案影响的平均场星系发电机的探索，在这里继续进行渐近解。所用的平均场发电机模型将标准理论推广到包括平均电动势对平均磁场和湍流参数（时间非定域性，或 Au}效应）。所考虑的发电机上的螺旋图案的效果是在螺旋形区域（其可以重叠的气体螺旋臂或位于臂间区域）的{α}效应的增强。平均磁场的轴对称和受控的非轴对称模式进行了研究半解析澄清和加强的数值结果。良好的定性协议之间的渐近解和数值解的文件I的全球性，刚性旋转的材料螺旋（密度波）。在除了共旋半径之外的所有银河系中心距离上，我们发现磁臂在方位角上偏离{α}臂，因此磁场强度的脊比{α}臂缠绕得更紧。此外，有限发电机弛豫时间的影响{ Au}（与湍流相关时间有关）的作用是使磁臂在与星系自转相反的方向上发生相移，即使在共旋半径处也是如此。这种机制可以用来解释在某些旋涡星系中观测到的磁臂和物质臂之间的相移。
The exploration of mean-field galactic dynamos affected by a galactic spiral pattern, begun in Chamandy et al. (2013, hereafter Paper I) with numerical simulations, is continued here with an asymptotic solution. The mean-field dynamo model used generalizes the standard theory to include the delayed response of the mean electromotive force to variations of the mean magnetic field and turbulence parameters (the temporal non-locality, or { au} effect). The effect of the spiral pattern on the dynamo considered is the enhancement of the {alpha}-effect in spiral-shaped regions (which may overlap the gaseous spiral arms or be located in the interarm regions). The axisymmetric and enslaved non-axisymmetric modes of the mean magnetic field are studied semi-analytically to clarify and strengthen the numerical results. Good qualitative agreement is obtained between the asymptotic solution and numerical solutions of Paper I for a global, rigidly rotating material spiral (density wave). At all galactocentric distances except for the co-rotation radius, we find magnetic arms displaced in azimuth from the {alpha}-arms, so that the ridges of magnetic field strength are more tightly wound than the {alpha}-arms. Moreover, the effect of a finite dynamo relaxation time { au} (related to the turbulence correlation time) is to phase-shift the magnetic arms in the direction opposite to the galactic rotation even at the co-rotation radius. This mechanism can be used to explain the phase shifts between magnetic and material arms observed in some spiral galaxies.
影响因子：
4.8
作者：
F. Gent;A. Shukurov;G. Sarson;A. Fletcher;M. Mantere
通讯作者：
F. Gent;A. Shukurov;G. Sarson;A. Fletcher;M. Mantere