Orbital dynamics of three-dimensional bars — III. Boxy/peanut edge-on profiles

Abstract

We present families, and sets of families, of periodic orbits that provide building blocks for boxy and peanut (hereafter b/p) edge-on profiles. We find cases where the b/p profile is confined to the central parts of the model and cases where a major fraction of the bar participates in this morphology. A b/p feature can be built either by 3D families associated with 3D bifurcations of the x1 family, or, in some models, even by families related with the z-axis orbits and existing over large energy intervals. The 'X' feature observed inside the boxy bulges of several edgeon galaxies can be attributed to the peaks of successive x1v1 orbits, provided their stability allows it. However in general, the x1v1 family has to overcome the obstacle of a S → → S transition in order to support the structure of a b/p feature. Other families that can be the backbones of b/p features are x1v4 and z3.1s. The morphology and the size of the boxy or peanut-shaped structures we find in our models are determined by the presence and stability of the families that support b/p features. The present study favours the idea that the observed edge-on profiles are the imprints of families of periodic orbits that can be found in appropriately chosen Hamiltonian systems, describing the potential of the bar.

Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

“…At T=5 Gyr (shown in the figure), in both cases, this has resulted in a pronounced B/P/X edge-on morphology. The vertical evolution lacks therapid buckling phase often reported in the literature (Raha et al 1991), in which sense it is more reminiscentof the resonance heating models (Quillen et al 2014), where the X is associatedwith disk stars heated by the 2:1 vertical resonance (Combes et al 1990;Pfenniger & Friedli 1991;Patsis et al 2002). Most importantly for the current study, the face-on morphology for = B D 0.08 is similar to that in massive barred galaxies, with a dominant, round barlens structure and a weak, thin bar component (compare to NGC 4548 in the lowermost row; see for classification of observed barlens categories): this structure survived to the end of the simulation (12 Gyr).…”

A Unified Framework for the Orbital Structure of Bars and Triaxial Ellipsoids

“…As pointed out previously by Pfenniger & Friedli (1991), the banana and antibanana orbits are vertical bifurcations of the x1 family (as can be seen from their x-y projections in the left-hand column). These orbits are referred to as the x1v1 family by Patsis et al (2002). Orbits like those in the second row of Figure 3 are boxy-bananas: they have a banana shape in x-z associated with 2:0:−1 resonance.…”

“…Vertical bifurcations of the x1 orbit associated with the 2: −2:−1 resonance may be responsible for the "X-shaped" structures seen in buckled edge-on bars (Patsis et al 2002;Athanassoula 2005). Patsis & Katsanikas (2014a, 2014b) also present a dynamical mechanism for building X-shaped peanuts with families of periodic orbits that are not bifurcations of x1 orbits.…”

“…The realization that bars can also undergo buckling instabilities (Combes & Sanders 1981;Raha et al 1991), which makes them develop substantial vertical thickness and peanut-shaped morphologies, led to the study of periodic orbits in three-dimensional bars (Pfenniger 1984;Martinet & de Zeeuw 1988;Pfenniger & Friedli 1991;Skokos et al 2002aSkokos et al , 2002b. It was shown that theappearance of specific morphological features in images of bars, such as the X-shape and peanut features seen in edge-on bars and the boxy/rectangular isophotes and "ansae" of face-on bars, could be explained by orbits trapped around specific periodic orbit families (Patsis et al 2002(Patsis et al , 2003(Patsis et al , 2010. The introduction of a thirddimension did not drastically change the picture of the nature of periodic orbits, and it was found that 3D bars are composed primarily of vertical bifurcations (resonances) of the x1 family and a few additional families (e.g., Pfenniger & Friedli 1991;Skokos et al 2002aSkokos et al , 2002b.…”

Measuring the X-shaped structures in edge-on galaxies

“…This scenario was first obtained in the N-body simulations by Combes & Sanders (1981), who found that the B/PS-bulges were formed shortly after the bar formation. Patsis, Skokos & Athanassoula (2002) studied the formation of the X-shaped structures from the point of view of individual orbits and found a set of orbit families, a combination of which appears to be X-shaped when viewed edge-on. The evolution of the bar vertical shape including the development of the X-shaped appearance as a result of a recurrent buckling, is demonstrated in Martinez-Valpuesta, Shlosman & Heller (2006).…”