Ordered and chaotic spiral arms

Abstract

The stellar flow at the arms of spiral galaxies is qualitatively different among different morphological types. The stars that reinforce the spiral arms can be either participating in an ordered or in a chaotic flow. Ordered flows are associated with normal (non-barred) spiral galaxies. Typically they are described with precessing ellipses corresponding to stable periodic orbits at successive energies (Jacobi constants). On the contrary, the spiral arms in barred-spiral systems may be supported by stars in chaotic motion. The trajectories of these stars are associated with the invariant manifolds of the unstable Lagrangian points (L1,2). Response and orbital models indicate that this kind of spirals either stop at an azimuth smaller than π/2, or present large gaps at about this angle. Chaotic spirals appear in strong bars having (L1,2) close to the ends of the bar. The arms of barred-spiral systems with corotation away from the end of the bar can be either as in the case of normal spirals, or supported by banana-like orbits surrounding the stable Lagrangian points (L4,5). We find also models combining ordered and chaotic flows.

Stellar Orbital Studies in Normal Spiral Galaxies. I. Restrictions to the Pitch Angle

“…Concerning to large scale structures in galaxies, these seem to be related mainly to ordered orbital behavior (Patsis 2008). This is the case for example, of grand design galaxies, where non-axisymmetric structures are composed by material librating around the family of periodic orbits known as X 1 (Contopoulos 2002).…”