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NGC 1300 dynamics – III. Orbital analysis

Authors

  • P. A. Patsis,

    Corresponding author
    1. Research Centre for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-115 27 Athens, Greece
    2. Observatoire Astronomique de Strasbourg, 11 rue de l’Université, 67000 Strasbourg, France
    3. European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
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  • C. Kalapotharakos,

    Corresponding author
    1. Research Centre for Astronomy, Academy of Athens, Soranou Efessiou 4, GR-115 27 Athens, Greece
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  • P. Grosbøl

    Corresponding author
    1. European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
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  • Based on observations collected at the European Southern Observatory, Chile: programme ESO 69.A-0021.

E-mail: patsis@academyofathens.gr (PAP); ckalapot@phys.uoa.gr (CK); pgrosbol@eso.org (PG)

ABSTRACT

We present the orbital analysis of four response models that succeed in reproducing morphological features of NGC 1300. Two of them assume a planar (2D) geometry with Ωp= 22 and 16 km s−1 kpc−1, respectively. The two others assume a cylindrical (thick) disc and rotate with the same pattern speeds as the 2D models. These response models reproduce most successfully main morphological features of NGC 1300 among a large number of models, as became evident in a previous study. Our main result is the discovery of three new dynamical mechanisms that can support structures in a barred spiral grand design system. These mechanisms are presented in characteristic cases, where these dynamical phenomena take place. They refer first to the support of a strong bar, of ansae type, almost solely by chaotic orbits, then to the support of spirals by chaotic orbits that for a certain number of pattern revolutions follow an n:1 (n= 7, 8) morphology, and finally to the support of spiral arms by a combination of orbits trapped around L4, 5 and sticky chaotic orbits with the same Jacobi constant. We have encountered these dynamical phenomena in a large fraction of the cases we studied as we varied the parameters of our general models, without forcing in some way their appearance. This suggests that they could be responsible for the observed morphologies of many barred spiral galaxies. Comparing our response models among themselves we find that the NGC 1300 morphology is best described by a thick-disc model for the bar region and a 2D disc model for the spirals, with both components rotating with the same pattern speed Ωp= 16 km s−1 kpc−1. In such a case, the whole structure is included inside the corotation of the system. The bar is supported mainly by regular orbits, while the spirals are supported by chaotic orbits.

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