The building blocks of 3D models of barred galaxies

I. The case of ring galaxies

¹ Research center for Astronomy and Applied Mathematics, Academy of Athens, Soranou Efessiou 4, 115 27 Athens, Greece
² School of Mathematics, University of Bristol, Fry Building, Woodland Road, Bristol BS8 1UG, UK

^⋆ Corresponding authors: mharsoul@academyofathens.gr, mkatsan@academyofathens.gr

Received: 17 March 2025
Accepted: 13 May 2025

Abstract

We make an orbital study of a Milky Way-like model of a barred galaxy of three degrees of freedom, with a relatively small bar perturbation (12% in forces). We find the planar PL_1, 2 family of orbits, which is the continuation of the Lagrangian equilibrium points, L_1, 2, for energy levels above E_nL1, 2, and study its stability indices, b₁, b₂. Then with the help of the 4D Poincaré surfaces of section (PSSs) of the 6D phase space in several energy levels, we find 3D sticky chaotic orbits lying above (having a small third dimension) the planar PL₂ orbits, as well as above other planar unstable periodic orbits, outside corotation, that behave like regular ones and support ring structures of R₁ and R₁R₂ type (on the plane of rotation) for a very long time compared to the Hubble time. We find that these sticky chaotic orbits quickly get diffused outside the system after tens or hundreds of Hubble times through a superdiffusing procedure that lasts for a certain time period, and that they will finally escape from the system through an Archimedean spiral converging to ballistic motion.