Regular and chaotic motion in elliptical galaxies

TL;DR

This paper reviews the dynamics of regular and chaotic orbits in elliptical galaxies, highlighting the construction of stable triaxial systems with chaotic orbits, the spatial distribution of different chaotic orbit types, and the role of slow figure rotation.

Contribution

It demonstrates the possibility of stable triaxial elliptical galaxy models with significant chaotic orbits and clarifies distinctions among orbit types and their spatial distributions.

Findings

Highly stable triaxial models can include large fractions of chaotic orbits.

Partially and fully chaotic orbits occupy different spatial regions.

Slow figure rotation is common in flattened models from cold collapses.

Abstract

Here I review recent work, by other authors and by myself, on some particular topics related to the regular and chaotic motion in elliptical galaxies. I show that it is quite possible to build highly stable triaxial stellar systems that include large fractions of chaotic orbits and that partially and fully chaotic orbits fill different regions of space, so that it is important not to group them together under the single denomination of chaotic orbits. Partially chaotic orbits should not be confused with weakly fully chaotic orbits either, and their spatial distributions are also different. Slow figure rotation (i.e., rotation in systems with zero angular momentum) seems to be always present in highly flattened models that result from cold collapses, with the rotational velocity diminishing or becoming negligibly small for less flattened models. Finally, I comment on the usefulness and limitation of the classification of regular orbits via frequency analysis.