Numerical modelling of Auriga’s Wheel – a new ring galaxy




We model the formation of Auriga’s Wheel – a recently discovered collisional ring galaxy. Auriga’s Wheel has a number of interesting features including a bridge of stars linking the neighbouring elliptical to the ring galaxy, and evidence for components of expansion and rotation within the ring. Using N-body/smoothed particle hydrodynamics modelling, we study collisions between an elliptical galaxy and a late-type disc galaxy. A near direct collision, with a mildly inclined disc, is found to reasonably reproduce the general system morphology ∼50 Myr following the collision. The collision must have a relatively low velocity (initially ∼150 km s−1) in order to form the observed bridge, and simultaneously match the galaxies separation. Our best-match model suggests the total disc galaxy is ∼5 times more massive than the elliptical. We find that the velocity of expansion of the ring is sensitive to the mass of the elliptical, while insensitive to the encounter velocity. We evolve our simulation beyond the current epoch to study the future destiny of the galaxy pair. In our model, the nucleus moves further away from the plane of the ring in the direction of the stellar bridge. The nucleus eventually merges with the elliptical galaxy ∼100 Myr after the present time. The ring continues to expand for ∼200 Myr before collapsing back. The low initial relative velocity of the two galaxies will eventually result in a complete merger.