Can Dust Destabilise Galactic Disks?

Abstract

We studied the dynamic influence of a dust component on the gaseous phase in central regions of galactic disks. We performed two-dimensional hydrodynamic simulations for flat, multicomponent disks embedded in a stellar and dark matter potential. The pressure-free dust component is coupled to the gas by a drag force depending on their velocity difference. 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 those regions the dust-free disks become most unstable for a small range of high azimuthal modes (m ∼ 8), whereas in dusty disks all modes have similar amplitudes resulting in a patchy appearance. The structures in the dust have a larger contrast between arm and interarm 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. This leads to a large scatter in the dust to gas ratios. The appearance of the dust is more cellular (i.e. sometimes connecting different spiral features), whereas the gas is organised in a multi-armed spiral structure. We found that an admixture of 2% dust (relative to the mass of the gas) destabilises 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 the saturation level after 30 Myr.