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Spiral instabilities: linear and non-linear effects
Ist Teil von
Monthly notices of the Royal Astronomical Society, 2021-02, Vol.500 (4), p.5043-5055
Ort / Verlag
Oxford University Press
Erscheinungsjahr
2021
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
ABSTRACT
We present a study of the spiral responses in a stable disc galaxy model to co-orbiting perturbing masses that are evenly spaced around rings. The amplitudes of the responses, or wakes, are proportional to the masses of the perturbations, and we find that the response to a low-mass ring disperses when it is removed – behaviour that is predicted by linear theory. Higher mass rings cause non-linear changes through scattering at the major resonances, provoking instabilities that were absent before the scattering took place. The separate wake patterns from two rings orbiting at differing frequencies produce a net response that is an apparently shearing spiral. When the rings have low mass, the evolution of the simulation is both qualitatively and quantitatively reproduced by linear superposition of the two separate responses. We argue that apparently shearing transient spirals in simulations result from the superposition of two or more steadily rotating patterns, each of which is best accounted for as a normal mode of the non-smooth disc.