Invariant manifolds as building blocks for the formation of spiral arms and rings in barred galaxies

TL;DR

This paper introduces a dynamical systems theory using invariant manifolds to explain the formation of spiral arms and rings in barred galaxies, linking galaxy morphology to orbital chaos and specific orbit types.

Contribution

It extends celestial mechanics techniques to galactic dynamics, providing a new framework to understand galaxy structures through invariant manifolds and orbit types.

Findings

R1 rings are linked to heteroclinic orbits.

R1R2 rings are associated with homoclinic orbits.

Spiral arms and R2 rings form without heteroclinic or homoclinic orbits.

Abstract

We propose a theory to explain the formation of spiral arms and of all types of outer rings in barred galaxies, extending and applying 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.