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Global m=1 instabilities and lopsidedness in disc galaxies

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Abstract
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 centre out to the radius where non-rotating waves are stabilized by the model's outwardly rising Q profile.
Keywords
MODES, STARS, instabilities, galaxies : kinematics and dynamics, galaxies : spiral, galaxies : structure, ECCENTRIC GRAVITATIONAL INSTABILITIES, COUNTERROTATING STELLAR DISKS, DWARF ELLIPTIC GALAXIES, OFF-CENTER NUCLEI, SPIRAL GALAXIES, STABILITY, SYSTEMS, ACCRETION

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Citation

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MLA
Dury, Vanessa, Sven De Rijcke, Victor P Debattista, et al. “Global M=1 Instabilities and Lopsidedness in Disc Galaxies.” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 387.1 (2008): 2–12. Print.
APA
Dury, V., De Rijcke, S., Debattista, V. P., & Dejonghe, H. (2008). Global m=1 instabilities and lopsidedness in disc galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 387(1), 2–12.
Chicago author-date
Dury, Vanessa, Sven De Rijcke, Victor P Debattista, and Herwig Dejonghe. 2008. “Global M=1 Instabilities and Lopsidedness in Disc Galaxies.” Monthly Notices of the Royal Astronomical Society 387 (1): 2–12.
Chicago author-date (all authors)
Dury, Vanessa, Sven De Rijcke, Victor P Debattista, and Herwig Dejonghe. 2008. “Global M=1 Instabilities and Lopsidedness in Disc Galaxies.” Monthly Notices of the Royal Astronomical Society 387 (1): 2–12.
Vancouver
1.
Dury V, De Rijcke S, Debattista VP, Dejonghe H. Global m=1 instabilities and lopsidedness in disc galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. 2008;387(1):2–12.
IEEE
[1]
V. Dury, S. De Rijcke, V. P. Debattista, and H. Dejonghe, “Global m=1 instabilities and lopsidedness in disc galaxies,” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol. 387, no. 1, pp. 2–12, 2008.
@article{426388,
  abstract     = {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 centre out to the radius where non-rotating waves are stabilized by the model's outwardly rising Q profile.},
  author       = {Dury, Vanessa and De Rijcke, Sven and Debattista, Victor P and Dejonghe, Herwig},
  issn         = {0035-8711},
  journal      = {MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY},
  keywords     = {MODES,STARS,instabilities,galaxies : kinematics and dynamics,galaxies : spiral,galaxies : structure,ECCENTRIC GRAVITATIONAL INSTABILITIES,COUNTERROTATING STELLAR DISKS,DWARF ELLIPTIC GALAXIES,OFF-CENTER NUCLEI,SPIRAL GALAXIES,STABILITY,SYSTEMS,ACCRETION},
  language     = {eng},
  number       = {1},
  pages        = {2--12},
  title        = {Global m=1 instabilities and lopsidedness in disc galaxies},
  url          = {http://dx.doi.org/10.1111/j.1365-2966.2008.13215.x},
  volume       = {387},
  year         = {2008},
}

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