Galaxies: from Kinematics to Dynamics

As will be apparent to anyone reading this book, the practitioners of N-body simulations have an enormous variety of preoccupations. Some are essentially pure mathematicians, who view the field as an exciting application for abstruse theory. Others enjoy formulating and tackling mathematically-neat problems, with little concern over whether the particular restrictions that they impose are also respected by nature. Still others are closer to computer scientists, inspired by the challenge of developing ever more sophisticated algorithms to tackle the N-body problem, but showing less interest in the ultimate application of their codes to solving astrophysical problems. This contribution is presented from yet another biased perspective: that of the observational galactic dynamicist. Observational astronomers tend to use N-body simulations in a rather cavalier manner, both as a tool for interpreting existing astronomical data, and as a powerful technique by which new observations can be motivated. The aim of this article is to illustrate this profitable interplay between simulations and observations in the study of galaxy dynamics, as well as highlighting a few of its shortcomings.