Chapter VI. Structures of Magnetic Fields in the Universe and Galaxies

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Abstract
Statistical analyses are made of ninety eight polarized extragalactic radio sources with known redshifts and rotation measures of the Faraday rotation. Distribution diagrams of the rotation measures and the redshifts reveal substantial conditions of a metagalactic magnetic field to the observed Faraday rotations for distant sources. The most probable direction of the metagalactic magnetic field is determined as l = 110°, b = 15° by using sixty one radio sources of |b| ≧ 35° selected out of these ninety eight data, where l and b denote new galactic longitude and latitude, and the polarized radio waves from the sources of |b| ≧ 35° have comparatively small galactic Faraday rotation effects. It is concluded that a large-scale metagalactic magnetic field is uniform at least up to a distance of z = 2 and the field strength is 2 × 10−9 gauss if Ne = 10−5 electrons cm−3 in the metagalactic space. Some upper limits on the amount of antimatter have been obtained from these results and it is concluded that the universe up to z = 2 is largely deviated from symmetry with respect to matter and antimatter. The existence of metagalactic magnetic field and recent theories on formation of galaxies suggest that magnetic fields in the Galaxy and galaxies are due to the frozen-in nature of the metagalactic magnetic field in condensing protogalaxies. Magnetic field structures at the level of the Galaxy and galaxies are also discussed. A circular arm with elliptical cross-section is used as a model of the spiral arm, and it is shown that interstellar gas may flow in a helical path along the axis of the arm. Interstellar helical magnetic lines of force can be in a stationary state, if such non-circular (rolling) motions of gas are superposed on galactic rotation. On the basis of the λ21-cm line survey of galactic plane by Westerhout (1966, 1969), we have searched for the dynamically postulated rolling motion. Distribution diagrams of the rolling motion along the arm suggested that the helical magnetic field is generated where the rolling motion changes its magnitude rapidly along the arm. Magnetic field topologies in the Magellanic-type barred galaxy are investigated from a magneto-hydrodynamical point of view and are compared with recently measured E-vectors of polarized starlight from the Large Magellanic Cloud. It seems very probable that a magnetized interstellar gas performs a large-scale circulation in the bar and magnetic lines of force are parallel to the stream lines.

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