The orbital content of bars: the origin of ‘non-x1-tree’, bar-supporting orbits

Abstract

Recently, many orbital studies in barred galaxy potentials have revealed the existence of orbits which are not trapped around x1-tree orbits, but could be potentially appropriate building blocks for bars. These findings question the uniqueness of the x1 family as the standard paradigm of orbital motion in galactic bars. The main goal of this paper is to investigate the role that such orbits could play in shaping the morphology of bars. We trace the morphological patterns appearing in the face-on and edge-on views of the non-periodic orbits presented in these studies and we show that they are introduced in the system by second type ("deuxième genre") bifurcations of x1. For this purpose, we use a typical 3D Ferrers bar model and follow the radial and vertical bifurcations of the x1 family considered as being mul-periodic, with mul = 2, 3, 5. The variation of the stability indices of x1 in the mul = 2, 3 cases give us also the 4− and 6−periodic orbits, respectively. We tabulate these orbits including all information necessary to assess their role as appropriate building blocks. We discuss their stability and their extent, as well as their size and morphological evolution, as a function of energy. We conclude that even the most important of the mul-periodic orbits presented in Tables 2 to 5 are less appropriate building blocks for bars than the families of the x1-tree at the same energy.

Orbital ingredients for cooking X-structures in edge-on galaxies

“…We begin this section with a general description of the distribution of the orbits over the ratio f z / f x . In the following subsections, we describe the specific spatial 3 Perhaps they are related to the orbits in figure A6 in Patsis & Athanassoula (2019).…”

“…and different types of chaotic orbits are studied. Some of these orbits can constitute the backbone of B/PS bulges and can delineate X-structures (Pfenniger 1984;Pfenniger & Friedli 1991;Skokos et al 2002;Patsis et al 2002a,b;Patsis & Katsanikas 2014a,b;Patsis & Harsoula 2018;Patsis & Athanassoula 2019). Usually, periodic and quasi-periodic orbits are calculated in analytic potentials representing a disk, a bar, and a bulge.…”

“…1 . Recently, the origin of 'non-x1-tree', bar-supporting orbits, the so-called mul-periodic orbits, has been studied in Patsis & Athanassoula (2019). Most of these orbits can be associated with resonant boxlet orbits from N-body simulations and they have a side-on shape, different from a 'banana' or an infinity sign.…”

First direct identification of the barlens vertical structure in galaxy models

“…Banana-like orbits ( f z / f x = 2.0 ± 0.05) delineate the most remote parts of a bar (e.g. Valluri et al 2016 andPatsis &Athanassoula 2019). They appear as two distant shell-like features in the xz unsharp-masked plot for the x1-like component.…”

First direct identification of the barlens vertical structure in galaxy models

“…In the unsharp-masked xz plot for the 'x1-like' orbital group, this structure reveals itself as a flat subsystem. Banana-like orbits ( f z / f x = 2.0 ± 0.05) delineate the most remote parts of a bar (e.g., Valluri et al 2016;Patsis & Athanassoula 2019). They appear as two distant shelllike features in the xz unsharp-masked plot for the x1-like component.…”