Are galactic disks dynamically influenced by dust?

¹ Institut für Theoretische Physik und Astrophysik d. Univ. Kiel, 24098 Kiel, Germany
² Institut für Astronomie d. Univ. Wien, Türkenschanzstr. 17, 1180 Wien, Austria
³ Institute of Physics, Stachki 194, Rostov-on-Don, Russia e-mail: orlova@rsusu1.rnd.runnet.ru
⁴ Isaak Newton Institute of Chile, Rostov-on-Don Branch

Corresponding author: Ch. Theis, theis@astro.univie.ac.at

Accepted: 26 February 2004

Abstract

Dynamically cold components are well known to destabilize hotter, even much more massive components. E.g. stellar disks can become unstable by a small admixture of cold gas or proto-planetary disks might be destabilized by a small fraction of dust. In this paper we studied the dynamical influence of a cold dust component on the gaseous phase in the central regions of galactic disks. We performed two-dimensional hydrodynamical simulations for flat multi-component disks embedded in a combined static stellar and dark matter potential. The pressure-free dust component is coupled to the gas by a drag force depending on their velocity difference.
It turned out that the most unstable regions are those with either a low or near to minimum Toomre parameter or with rigid rotation, i.e. the central area. In that regions the dust-free disks become most unstable for high azimuthal modes (), whereas in dusty disks all modes have a similar amplitude resulting in a patchy appearance. The structures in the dust have a larger contrast between arm and inter-arm regions than those of the gas. The dust peaks are frequently correlated with peaks of the gas distribution, but they do not necessarily coincide with them. Therefore, a large scatter in the dust-to-gas ratios is expected. The appearance of the dust is more cellular (i.e. sometimes connecting different spiral features), whereas the gas is organized in a multi-armed spiral structure.
We found that an admixture of 2% dust (relative to the mass of the gas) destabilizes gaseous disks substantially, whereas dust-to-gas ratios below 1% have no influence on the evolution of the gaseous disk. For a high dust-to-gas ratio of 10% the instabilities reach a saturation level already after 30 Myr. The stability of the gaseous disks also strongly depends on their Toomre parameter. But even in hot gaseous disks a destabilizing influence of the dust component has been found.