ISSN:
1572-946X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract We show that magnetic fields can be important in the formation and evolution of galaxies and that they might be indeed the missing parameters to explain the Hubble sequence. We use the self-consistent theory of spiral magneto-hydrodynamic flow developed by Henriksen and co-workers over the last few years. Section 2 is a short outline of this theory, where we introduce and justify the simplifying assumptions and list the relevant physical relations. Section 3 deals mainly with the formation of galactic nuclei and proto-galaxies. We envisage the following scenario: The first objects to form after recombination in a canonical hot big-bang universe with turbulence and magnetic fields have masses of order 109 M ⊙. In a violent burst of activity—possible mechanisms are discussed—they ionize the surrounding medium, raising the Jeans mass to a galactic scale, and becoming the condensation seeds of galaxies. The subsequent evolution of these nuclei, including recurrent activity, is discussed in some detail. The remaining sections—in principle independent from Section 3—deal with galactic morphology as the result of the collapse of a hot, spherical, rotating proto-galaxy endowed with a regular magnetic field. The main parameter determining the morphological type is the anglei between the magnetic field and the angular momentum. Smalli give rise to Sc galaxies, largei to ellipticals (Section 4), and intermediate values to the rest of the Hubble sequence. Subtypes are produced by variation of the strength of the magnetic field in comparison to the angular momentum. Thus relatively strong fields will produce triaxial ellipticals, barred spirals and irregulars. Some of the observationally testable predictions of our theory concern: the energetics, duration and frequency of nuclear activity, the absence of dwarf spiral galaxies, rigidly rotating nuclear regions in galaxies, the mass and structure of galactic halos, leading and trailing spiral arms and their pitch angle, the bulge-to-disc ratio, the frequency distribution of morphological types, and the warping of galactic discs. Moreover some seemingly pathological galaxies like NGC 2685 and 4314 find a simple explanation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00647074
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