Journal Article

Regular and chaotic orbits in barred galaxies – I. Applying the SALI/GALI method to explore their distribution in several models

T. Manos and E. Athanassoula

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 415, issue 1, pages 629-642
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18734.x
Regular and chaotic orbits in barred galaxies – I. Applying the SALI/GALI method to explore their distribution in several models

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The distinction between the chaotic and regular behaviour of orbits in galactic models is an important issue and can help our understanding of galactic dynamical evolution. In this paper, we deal with this issue by applying the Smaller ALingment Index (SALI) and Generalized ALingment Index (GALI) techniques to extensive samples of orbits obtained by integrating numerically the equations of motion in a barred galaxy potential. We estimate first the fraction of chaotic and regular orbits for the 2 degrees of freedom (d.o.f.) case [where the galaxy extends only in the (x, y) space] and show that it is a non-monotonic function of the energy. For the 3-d.o.f. extension of this model (in the z-direction), we give similar estimates, both by exploring different sets of initial conditions and by varying the model parameters, like the mass, size and pattern speed of the bar. We find that regular motion is more abundant at small radial distances from the centre of the galaxy, where the relative non-axisymmetric forcing is relatively weak, and at small distances from the equatorial plane, where the trapping around the stable periodic orbits is important. We also find that the variation in the bar pattern speed, within a realistic range of values, does not affect much the phase-space fraction of regular and chaotic motions. Using different sets of initial conditions, we show that chaotic motion is dominant in galaxy models whose bar component is more massive, while models with a fatter or thicker bar present generally more regular behaviour. Finally, we find that the fraction of orbits that are chaotic correlates strongly with the bar strength.

Keywords: galaxies: kinematics and dynamics; galaxies: structure

Journal Article.  10061 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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