1996A&A...311..397J

A 3D computer code with particles simulating motions and interactions of giant molecular clouds (GMC) is used to tackle several problems related to the existence of molecular rings observed in many spiral galaxies. In particular, we suggest that unbarred (SA) galaxies possessing a gaseous ring have a very weak unresolved oval distortion in their center: we are able to generate a conspicuous ring in much weaker bars (∼1% of the axisymmetric field) than previous models did. At the same time, we easily get multiple (up to 3) rings connected to different resonances (ILR, 2/1, 4/1, 6/1, OLR), depending on the bar angular speed. Inelastic collisions of GMCs play the key role in our simulations. We use a simple sticky-particles scheme in which the inelasticity is specified in terms of two parameters, β_r and β_t, that multiply the components of the relative cloud-cloud velocity (parallel and perpendicular to the line joining the clouds). This approach was frequently used in the past by many authors, however the coverage of all conceivable values of β's was never done, and rarely more than one rather arbitrary combination (β_r,β_t) was used to derive results. To fill this gap, we compare the output of our simulations for a wide range of (β_r,β_t) and find that it can significantly vary. We also propose to extend admissible values of β_r to allow the passage of gaseous clouds one through another, while previous models have always made the clouds rebounce after a collision.