Regular motions in double bars. II. Survey of trajectories and 23 models

TL;DR

This paper investigates the stability and structure of double bars in galaxies by analyzing trajectories and models, revealing the significance of stable double-frequency orbits and challenging the role of resonant coupling in reducing chaos.

Contribution

The study provides a comprehensive survey of stable double-frequency orbits in double bar systems and introduces a method to quantify phase-space trapping and regular motions.

Findings

Stable double-frequency orbits form the backbone of double bars.

Resonant coupling may not significantly reduce chaos in double bar systems.

A new method to measure phase-space trapping around double-frequency orbits.

Abstract

We show that stable double-frequency orbits form the backbone of double bars, because they trap around themselves regular orbits, as stable closed periodic orbits do in single bars, and in both cases the trapped orbits occupy similar volume of phase-space. We perform a global search for such stable double-frequency orbits in a model of double bars by constructing maps of trajectories with initial conditions well sampled over the available phase-space. We use the width of a ring sufficient to enclose a given map as the indicator of how tightly the trajectory is trapped around a double-frequency orbit. We construct histograms of these ring widths in order to determine the fraction of phase-space occupied by ordered motions. We build 22 further models of double bars, and we construct histograms showing the fraction of the phase-space occupied by regular orbits in each model. Our models indicate that resonant coupling between the bars may not be the dominant factor reducing chaos in the system.