Instabilities in a nonstationary model of self-gravitating disks. III. The phenomenon of lopsidedness and a comparison of perturbation modes |
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| Authors: | K T Mirtadjieva S N Nuritdinov J K Ruzibaev Muhammad Khalid |
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| Institution: | 1.Astronomical Institute,Academy of Sciences of the Republic of Uzbekistan,Tashkent,Uzbekistan;2.Department of Astronomy and Astrophysics,National University of Uzbekistan,Tashkent,Uzbekistan;3.Federal University,Karachi,Pakistan |
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| Abstract: | This is an examination of the gravitational instability of the major large-scale perturbation modes for a fixed value of the
azimuthal wave number m = 1 in nonlinearly nonstationary disk models with isotropic and anisotropic velocity diagrams for
the purpose of explaining the displacement of the nucleus away from the geometric center (lopsidedness) in spiral galaxies.
Nonstationary analogs of the dispersion relations for these perturbation modes are obtained. Critical diagrams of the initial
virial ratio are constructed from the rotation parameters for the models in each case. A comparative analysis is made of the
instability growth rates for the major horizontal perturbation modes in terms of two models, and it is found that, on the
average, the instability growth rate for the m = 1 mode with a radial wave number N = 3 almost always has a clear advantage
relative to the other modes. An analysis of these results shows that if the initial total kinetic energy in an isotropic model
is no more than 12.4% of the initial potential energy, then, regardless of the value of the rotation parameter Ω, an instability
of the radial motions always occurs and causes the nucleus to shift away from the geometrical center. This instability is
aperiodic when Ω = 0 and is oscillatory when Ω ≠ 0 . For the anisotropic model, this kind of structure involving the nucleus
develops when the initial total kinetic energy in the model is no more than 30.6% of the initial potential energy. |
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