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Article Contents

ABSTRACT

1.INTRODUCTION
1.1.Historical overview

2.GENERATION OF SPIRAL STRUCTURE
2.1.Quasi-stationary density wave theory
2.1.1.Dispersion relations of tight-winding density waves
2.1.2.Propagation of tight-winding density waves
2.1.3.Swing amplification
2.1.4.Global mode theory
2.1.5.Simulations of long-lived spiral patterns
2.2.Dynamic spirals
2.2.1.Swing amplified spirals
2.2.2.Corotation scattering and radial migration of stars
2.2.3.Recurrent mechanisms for dynamic stellar spiral arms
2.3.Bar driven spirals
2.3.1.Spirals corotating with bars
2.3.2.Decoupling between spirals and bars
2.3.3.Non-linear coupling between spirals and bars
2.3.4.Non-stationary spiral arms in barred galaxies
2.4.Tidal interactions
2.4.1.Historical overview
2.4.2.Tidally induced arms: stationary, kinematic or material arms?
2.4.3.Prograde and retrograde encounters, and the orbit of the perturber
2.4.4.Longevity of tidally-induced spirals
2.5Stochastic star formation
2.6.Exotic mechanisms

3.BEHAVIOUR OF GAS IN SPIRAL GALAXIES
3.1.Stability of a star and gas disc
3.2.Damping of spiral arms
3.3.Physical processes in the ISM
3.4.Substructure along spiral arms
3.5.Quasi-stationary density waves
3.5.1.Resonances
3.5.2.Stability and structure of the shock
3.6.Tidally induced spiral arms
3.7.Gas flow in dynamic spiral arms

4.OBSERVATIONAL EVIDENCE FOR DIFFERENT MECHANISMS OF GENERATING SPIRAL STRUCTURE
4.1.Pattern speeds
4.2.Pitch angles
4.3.Stellar cluster ages
4.4.Resonances and interference patterns
4.5.Observations of grand design and flocculent structure
4.6.The Milky Way
4.7.Spiral arm triggering of star formation

5.SUMMARY AND DISCUSSION
5.1.Quasi-stationary density wave theory
5.2.Dynamic spirals
5.3.Tidal interactions
5.4.Bar driven spirals
5.5.Other mechanisms
5.6.Observations

REFERENCES