Adaptive mesh refinement simulations of collisional ring galaxies: effects of the interaction geometry

TL;DR

This study uses adaptive mesh refinement simulations to explore how the geometry of galaxy collisions influences the formation and properties of collisional ring galaxies, including star formation and observable features.

Contribution

It introduces new simulation techniques to analyze the effects of impact parameter, velocity, and inclination on ring galaxy formation and star formation history.

Findings

Axisymmetric encounters produce circular rings and short starbursts.

Off-centre interactions lead to asymmetric rings and prolonged star formation.

Simulated rings are bluer than the surrounding disc, matching observations.

Abstract

Collisional ring galaxies are the outcome of nearly axisymmetric high-speed encounters between a disc and an intruder galaxy. We investigate the properties of collisional ring galaxies as a function of the impact parameter, the initial relative velocity and the inclination angle. We employ new adaptive mesh refinement simulations to trace the evolution with time of both stars and gas, taking into account star formation and supernova feedback. Axisymmetric encounters produce circular primary rings followed by smaller secondary rings, while off-centre interactions produce asymmetric rings with displaced nuclei. We propose an analytical treatment of the disc warping induced by an inclination angle greater then zero. The star formation history of our models is mainly influenced by the impact parameter: axisymmetric collisions induce impulsive short-lived starburst episodes, whereas off-centre encounters produce long-lived star formation. We compute synthetic colour maps of our models and we find that rings have a B-V colour typically ~0.2 mag bluer than the inner and outer disc, in agreement with observations.