Spiral structure: M51
The generation of spiral structure is one of the longstanding problems in galactic evolution. The above image is from a simulation designed to model the Whirlpool Galaxy, M51. By modelling the passage of a companion galaxy (NGC 5195) with M51 it is possible to reproduce not just the global structure, but also kinks, and asymmetries peculiar to the particular orbit of M51. Such calculations are promising for future detailed studies of the ISM in nearby galaxies, for comparisons with projects such as PAWS, as well as ALMA.