Pattern Speeds in Interacting Galaxies
Dobbs, C. L., 2010, eprint arXiv:1002.1269, (Mem. S.A.It. Vol. 00, 107)
http://arxiv.org/abs/1002.1269v1
Spiral patterns are the arrangements that are known to exist in spiral galaxies and that can also form as a result of galaxies interacting with each other. They are known to be driven by bars, i.e. the central structure of some galaxies.
With the use of numerical simulations, Dobbs 2010 perform an investigation on the interaction between galaxies. The software that they used for the creation of the simulations is SPH (Smoothed Particle Hydrodynamics code) and they created a model for a galaxy interacting system.
The modeling of the interior of the galaxies was done under different initial conditions, and, even though the spiral arms exhibit different pattern speeds, these speeds decrease as with an increase in the radius.
The overall calculations were performed with different types of galaxies (related to their structure): stellar, gaseous, mixed stellar and gaseous, and the interaction with an orbiting galaxy. Across the disk of the resulting galaxy, the pattern speed is not constant in time, and they are also different for each arm. They find a maximum pattern speed of ~20km/s/kpc for the disks that have a live stellar component. The speed decreases by a factor of four at the end of the spiral arm. When only the gas is modeled, the speeds are in most cases very small (5 km/s/kpc) at all radii. Finally, when they do the simulation with mixed stellar and gaseous galaxies they noticed that the gas tends to follow the stellar distribution, thus increasing the pattern speeds.
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