Dynamics of thick, open spirals in Perlas potentials

Abstract

The PERLAS potential has been successfully used in many studies related with the dynamics of the spiral arms \textit{on} the equatorial plane of normal (non-barred) spiral galaxies. In the present work we extend these studies by investigating the three-dimensional dynamics of the spiral arms in the same type of potential. We consider a typical open, logarithmic, spiral pattern of pitch angle 25${}^{\circ }$ and we examine the stellar orbits that can support it as the ratio of the masses of the spiral over the disk component ($M_s/M_d$) varies. We indicate the families of `three-dimensional' periodic orbits that act as the backbone of the spiral structure and we discuss their stability in the models we present. We study further the quasi-periodic and non-periodic orbits in general that follow spiral-supporting orbits as the $M_s/M_d$ ratio increases. We find that a bisymmetric spiral with 25${}^{\circ }$ pitch angle is better supported by orbits in models with $0.03⪅M_s/M_d⪅0.07$. In these cases a strong spiral pattern is supported between the radial 2:1 and 4:1 resonances, while local enhancements of the imposed spirals are encountered in some models between 4:1 and corotation. A characteristic bar-like structure is observed in all models at radii smaller than the radius of the 2:1 resonance.

19 pages, 23 figures, accepted for publication in The Astrophysical Journal

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Cited by in corpus (3)

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• Precessing ellipses as the building blocks of spiral arms
• Chaoticity in the vicinity of complex unstable periodic orbits in galactic type potentials