Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-03-19
Astronomy and Astrophysics
Astrophysics
12 pages, 14 figures
Scientific paper
10.1111/j.1365-2966.2008.13215.x
Lopsidedness is common in spiral galaxies. Often, there is no obvious external cause, such as an interaction with a nearby galaxy, for such features. Alternatively, the lopsidedness may have an internal cause, such as a dynamical instability. In order to explore this idea, we have developed a computer code that searches for self-consistent perturbations in razor-thin disc galaxies and performed a thorough mode-analysis of a suite of dynamical models for disc galaxies embedded in an inert dark-matter halo with varying amounts of rotation and radial anisotropy. Models with two equal-mass counter-rotating discs and fully rotating models both show growing lopsided modes. For the counter-rotating models, this is the well-known counter-rotating instability, becoming weaker as the net rotation increases. The m=1 mode of the maximally rotating models, on the other hand, becomes stronger with increasing net rotation. This rotating m=1 mode is reminiscent of the eccentricity instability in near-Keplerian discs. To unravel the physical origin of these two different m=1 instabilities, we studied the individual stellar orbits in the perturbed potential and found that the presence of the perturbation gives rise to a very rich orbital behaviour. In the linear regime, both instabilities are supported by aligned loop orbits. In the non-linear regime, other orbit families exist that can help support the modes. In terms of density waves, the counter-rotating m=1 mode is due to a purely growing Jeans-type instability. The rotating m=1 mode, on the other hand, grows as a result of the swing amplifier working inside the resonance cavity that extends from the disc center out to the radius where non-rotating waves are stabilized by the model's outwardly rising Q-profile.
de Rijcke Sven
Debattista Victor P.
Dejonghe Herwig
Dury Vanessa
No associations
LandOfFree
Global m=1 instabilities and lopsidedness in disc galaxies does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Global m=1 instabilities and lopsidedness in disc galaxies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Global m=1 instabilities and lopsidedness in disc galaxies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-577277