Magnetic spiral arms in galaxies
Magnetic spiral arms in galaxies
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星系中的磁旋臂
DOI：
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发表时间：
1998
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影响因子：
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通讯作者：
A. Shukurov
中科院分区：
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作者：
A. Shukurov
螺旋星系中的大尺度磁场在螺旋形区域（磁臂）中最强。最近发现星系NGC 6946的磁臂可以与气体臂交织，而不是与它们重合。有迹象表明，磁臂和气体臂可能在其他星系中交叉。我们认为，磁臂可以远离气体密度较高的区域（气体臂），因为后者的星际湍流更强。我们预测在发电机较弱的星系中，磁臂与气体臂交织在一起，而在发电机较强的星系中，这两种螺旋结构应该重叠;在中间的情况下，磁和气体螺旋结构在星系内部重叠，在外部交织（可能是M51）。另一种产生位移的磁性和气体螺旋图案的可能机制是由于发电机对气体臂中湍流增强的响应延迟。这应该会导致磁臂和气体臂在共转半径处交叉，就像在星系IC 342和M83中可能观察到的那样。我们还认为，旋臂只有微弱的影响局部scaleheight的星系气体层。
Large-scale magnetic fields in spiral galaxies are strongest in spiral-shaped regions, the magnetic arms. It was recently discovered for the galaxy NGC 6946 that magnetic arms can be interlaced with the gaseous arms, rather than coinciding with them. There are indications that the magnetic and gaseous arms may cross in some other galaxies. We suggest that magnetic arms can be located away from regions of higher gas density (gaseous arms) because interstellar turbulence is stronger in the latter. We predict magnetic arms interlaced with gaseous arms in galaxies with weak dynamos, whereas the two spiral structures should overlap in galaxies with strong dynamo action; in an intermediate case, the magnetic and gaseous spiral structures overlap in the inner galaxy and are interlaced in the outer parts (as, possibly, in M51). Another plausible mechanism to produce displaced magnetic and gaseous spiral patterns results from a delay in the dynamo response to the enhancement of turbulence in the gaseous arms. This should lead to the magnetic and gaseous arms crossing at the corotation radius, as possibly observed in the galaxies IC 342 and M83. We also argue that spiral arms only weakly affect the local scaleheight of the galactic gas layer.