Tidal spiral arms in two-component galaxies - Density waves and swing amplification

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