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- Bertin, G., et al.
(författare)
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Global spiral modes in stellar disks containing gas
- 1988
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 195, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- The authors present a linear study of the role of gas on global spiral modes in stellar disks using a simple two-fluid model. The local destabilizing role of a cold component has been known for many years and calculated by various authors. The authors confirm the effectiveness of a small amount of gas in fueling spiral instabilities with a response which is primarily at short wavelengths by constructing a synthetic diagram which summarizes the local stability analysis. Then they proceed to consider global spiral modes in two-component systems with applications to regimes of astrophysical interest that are expected to be associated with normal spiral structure. Moderate growth spiral modes are found that are very close in structure to those of one-component systems, but for substantially higher values of the stability parameter Q. A simple model of self-regulation is also presented.
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| 8. |
- Sundelius, B., et al.
(författare)
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Tidal spiral arms in two-component galaxies - Density waves and swing amplification
- 1987
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 174:1-2, s. 67-77
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Tidskriftsartikel (refereegranskat)abstract
- The tidal spiral arms in galaxies are studied using the two-dimensional polar coordinate N-body program of Miller (1976, 1978) and a two-component disk galaxy perturbed by a point-mass model. The density wave theory, which explains spiral arms in the presence of differential rotation, and the components of the model and computer program are discussed. The spiral arms in the cold (spiral arm population) and hot (old stars) components and their velocity dispersions are examined, and consideration is given to density waves and swing amplification. The data reveal that a grand design spiral pattern can develop in the gaseous component of a disk galaxy as a result of tidal triggering from a companion, and the spiral pattern and kinematics of the particles correlate with predictions from the density wave theory.
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| 9. |
- Thomasson, Magnus, 1961, et al.
(författare)
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Formation of leading spiral arms in retrograde galaxy encounters
- 1989
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 211:1, s. 25-36
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Tidskriftsartikel (refereegranskat)abstract
- The formation of spiral structures in retrograde galaxy encounters was studied theoretically and with N-body simulations. A one-armed leading spiral dominates in a disk if the tidal perturbation from the retrograde companion is large enough, and the disk is surrounded by a massive halo. The leading arm is made up of particles in slightly elongated orbits, the turning points of which outline the arm. The orbits precess in such a way that the arm structure survives while it rotates in the opposite sense to the disk rotation. From the literature it is found that very few spirals in a sample of galaxies with a large companion have leading spiral arms. A possible reason for this is that very few spiral galaxies have a halo with larger mass than the disk mass.
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