| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1994: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1993: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
First, we obtained the rotation measure (RM) distribution and studied the configuration of magnetic fields in spiral galaxy M51, by analyzing the observed distribution of the linear poralization of radio waves. We confirmed that the configuration of magnetic fields in M51 was bisymmetric spiral (BSS) magnetic fields. The distribution of RM observed in M51 was compared with distribution of RM calculated for the model of BSS magnetic fields which was given by our provious papers. It is shwon that the configuration of magnetic fields in M51 was agree with that of BSS fields generated and maintained by the galactic dynamo.
Next, we simulated numericaly the motion of gas when BSS fields existed in the disk of a galaxy. The result of our numerical simulation showed that two gaseous spiral arms were formed near the local maxima of the azimuthal component of BSS fields for usual values of the magnetic field strength and gas density in spiral galaxies. It suggested that BSS fields have an import
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ant role of the origin and maintenance of spiral arms.
On the other hand, there are several reports that the growth rate of BSS fields sustained by the dynamo is lower than that of axisymmetric fields, and that BSS fields are localized in a quite narrow range of the galactic disk in radial direction. However, these reports were discussed with the usual dynamo (positive dynamo).
Finaly, we showed that BSS fields could exist in whole range of gaseous disk in radial direction although the growth rate was nearly zero, when we considered the negative dynamo which acted the opposite sense of the usual dynamo (positive dynamo). The reason that BSS fields can exist in spiral galaxies in spite of the low growth rate is as follows : The cosmic magnetic fields were trapped in protogalaxies and twisted by differential rotation, so BSS magnetic fields were formed in disk of protogalaxies. These BSS fields became seed fields for galactic dynamo and BSS magnetic fields have been maintained over a long period of time. We concluded that BSS fields in galaxies were maintained by the galactic dynamo action. Less
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