The formation of spiral arms and rings in barred galaxies

TL;DR

This paper introduces a new dynamical theory explaining the formation of spiral arms and rings in barred galaxies through chaotic orbital motion and invariant manifolds, linking galaxy morphology to underlying orbital structures.

Contribution

It extends celestial mechanics techniques to galactic dynamics, providing a novel explanation for galaxy structures based on invariant manifolds and chaotic orbits.

Findings

R1 rings linked to heteroclinic orbits

R1R2 rings linked to homoclinic orbits

Different galaxy morphologies explained by dynamical parameters

Abstract

We propose a new theory to explain the formation of spiral arms and of all types of outer rings in barred galaxies. We have extended and applied the technique used in celestial mechanics to compute transfer orbits. Thus, our theory is based on the chaotic orbital motion driven by the invariant manifolds associated to the periodic orbits around the hyperbolic equilibrium points. In particular, spiral arms and outer rings are related to the presence of heteroclinic or homoclinic orbits. Thus, R1 rings are associated to the presence of heteroclinic orbits, while R1R2 rings are associated to the presence of homoclinic orbits. Spiral arms and R2 rings, however, appear when there exist neither heteroclinic nor homoclinic orbits. We examine the parameter space of three realistic, yet simple, barred galaxy models and discuss the formation of the different morphologies according to the properties of the galaxy model. The different morphologies arise from differences in the dynamical parameters of the galaxy.