Rings and spirals in barred galaxies. II. Ring and spiral morphology

TL;DR

This paper develops a theory explaining the formation of rings and spirals in barred galaxies through orbit manifolds, successfully matching observed morphologies and predicting how galactic forces influence these structures.

Contribution

It introduces a new orbital manifold-based model that accounts for various ring and spiral morphologies observed in barred galaxies, including specific ring types and spiral arm characteristics.

Findings

Model reproduces observed ring morphologies such as R1, R2, and their combinations.

Theoretical and observed spiral shapes show strong agreement.

Stronger non-axisymmetric forces lead to more open and elliptical rings and spirals.

Abstract

In this series of papers, we propose a theory to explain the formation and properties of rings and spirals in barred galaxies. The building blocks of these structures are orbits guided by the manifolds emanating from the unstable Lagrangian points located near the ends of the bar. In this paper we focus on a comparison of the morphology of observed and of theoretical spirals and rings and we also give some predictions for further comparisons. Our theory can account for spirals as well as both inner and outer rings. The model outer rings have the observed $R_1$, $R_1'$, $R_2$, $R_2'$ and $R_1R_2$ morphologies, including the dimples near the direction of the bar major axis. We explain why the vast majority of spirals in barred galaxies are two armed and trailing, and discuss what it would take for higher multiplicity arms to form. We show that the shapes of observed and theoretical spirals agree and we predict that stronger non-axisymmetric forcings at and somewhat beyond corotation will drive more open spirals. We compare the ratio of ring diameters in theory and in observations and predict that more elliptical rings will correspond to stronger forcings. We find that the model potential may influence strongly the numerical values of these ratios.