Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...478..446k&link_type=abstract
Astrophysical Journal v.478, p.446
Astronomy and Astrophysics
Astronomy
10
Galaxies: Kinematics And Dynamics, Galaxies: Spiral, Galaxies: Structure
Scientific paper
We analyze the global modal properties of self-gravitating disks with exponential density distributions both in one- and three-component approaches. We take into account the observational properties of galactic disks, namely, that the radial dependence of the stellar velocity dispersion cs is proportional to the square of the stellar surface density. The stability properties of a one-component disk are determined mainly by its central velocity dispersion and its maximal rotational velocity. Disks with the central velocity dispersion less than unity in units G = Rd = Md = 1 are unstable to tightly wound spirals, if the minimal value of Toomre's Q-parameter is less than or close to unity. Here G is the gravitational constant, and Rd and Md are the radius and mass of the disk, respectively. Higher velocity dispersions increase the wavelength of unstable modes, as well as the probability of their generation. Disks with cs > 1.0 at the center can be unstable if the minimal value of the Q-parameter is less than 1.8. The stability of multicomponent disks is jointly determined by self-gravity and mass transformations between different phases. In this paper we discuss the situation in which the stability properties of the disk are primarily determined by self-gravity. If the admixture of clouds and gas are small, the shape and the growth rate of the principal unstable mode does not change significantly. However, a significant cold component in the system increases the value of the growth rate of an unstable mode. A new effect, in comparison to the one-component approach, is an angular phase separation between spirals of different components. Such displacements have been observed in the spiral arms of some nearby galaxies and can thus be considered as a confirmation of the validity of a global modal approach to self-gravitating multiphase galactic disks.
Kikuchi Naokichi
Korchagin Vladimir
Miyama Shoken M.
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