Regular motions in double bars. I. Double-frequency orbits and loops

TL;DR

This paper investigates the nature of particle orbits in double-barred galaxies, identifying double-frequency orbits as the main support structure, which map onto loops and differ from single-frequency orbits in single bars.

Contribution

It introduces the concept of double-frequency orbits in double bars and explains how these orbits form the backbone of the oscillating potential, extending the understanding of galactic bar dynamics.

Findings

Double-frequency orbits support double bars.

Orbits map onto loops that confine trapped trajectories.

No free oscillations are present in these orbits.

Abstract

Bars in galaxies are mainly supported by particles trapped around stable periodic orbits. These orbits represent oscillatory motion with only one frequency, which is the bar driving frequency, and miss free oscillations. We show that a similar situation takes place in double bars: particles get trapped around parent orbits, which in this case represent oscillatory motion with two frequencies of driving by the two bars, and which also lack free oscillations. Thus the parent orbits, which constitute the backbone of an oscillating potential of two independently rotating bars, are the double-frequency orbits. These orbits do not close in any reference frame, but they map onto loops, first introduced by Maciejewski & Sparke (1997). Trajectories trapped around the parent double-frequency orbit map onto a set of points confined within a ring surrounding the loop.