Mechanisms of the Vertical Secular Heating of a Stellar Disk

Abstract

We investigate the nonlinear growth stages of bending instability in stellar disks with exponential radial density profiles.We found that the unstable modes are global (the wavelengths are larger than the disk scale lengths) and that the instability saturation level is much higher than that following from a linear criterion. The instability saturation time scales are of the order of one billion years or more. For this reason, the bending instability can play an important role in the secular heating of a stellar disk in the $z$ direction. In an extensive series of numerical $N$-body simulations with a high spatial resolution, we were able to scan in detail the space of key parameters (the initial disk thickness $z_0$, the Toomre parameter $Q$, and the ratio of dark halo mass to disk mass $M_{\mathrm{h}}/M_{\mathrm{d}}$). We revealed three distinct mechanisms of disk heating in the $z$ direction: bending instability of the entire disk, bending instability of the bar, and heating on vertical inhomogeneities in the distribution of stellar matter.

arXiv comment22 pages including 8 figures. To be published in Astronomy Letters (v.29, 2003)

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• Sinking Satellites and the Heating of Galaxy Discs
• The Age of the Solar Neighbourhood
• The shape of the velocity ellipsoid in NGC 488
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• Gravitational scattering of stars and clusters and the heating of the Galactic disk
• What determines the flatness of X-shaped structures in edge-on galaxies
• The onset of warps in Spitzer observations of edge-on spiral galaxies
• Orbital ingredients for cooking X-structures in edge-on galaxies
• Bending instability in galactic discs. Advocacy of the linear theory
• Is the late buckling stage inevitable in the bar life?
• Gravitational instability and spatial regularity of the gas clouds and young stellar population in spiral arms of NGC 628
• Spectral Observations of Superthin Galaxies