Comparing gaseous and stellar orbits in a spiral potential

Abstract

It is generally assumed that gas in a galactic disc follows non-self-intersecting periodic stellar orbits closely. In order to test this common assumption, we have performed magnetohydrodynamics (MHD) simulations of a galactic-like disc under the influence of a spiral galactic potential. We have also calculated the actual orbit of a gas parcel and compared it to stable periodic stellar orbits in the same galactic potential and position. We found that the gaseous orbits approach periodic stellar orbits far from the major orbital resonances only. Gas orbits initialized at a given galactocentric distance but at different azimuths can be different, and scattering is conspicuous at certain galactocentric radii. Also, in contrast to the stellar behaviour, near the 4:1 (or higher order) resonance the gas follows nearly circular orbits, with much shorter radial excursions than the stars. Also, since the gas does not settle into a steady state, the gaseous orbits do not necessarily close on themselves. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.