Collisions of galaxies are often observed to produce increases in the far-IR flux and star formation rates, as compared to those seen in isolated galaxies. It is expected that the star formation taking place in these systems occurs under more violent circumstances than those found in the spiral arms of disk galaxies, for example. We will present some results from a study in which we have produced combined N-body/Smooth Particle Hydrodynamics simulations of collisions of galaxies, looking for regions in which shocks develop and where the gas density gets high enough that new star formation might be expected to take place. These results give us a preliminary idea of what the properties of the shocked, high density regions might be and provide a basis for the future inclusion of violent star formation into such calculations with a view to eventually explaining the observed enhancements.
In seeking out places in the present Universe where star formation might be expected to occur under more violent circumstances than those that occur in the arms of spiral galaxies one is drawn to consider the interiors of gas-rich galaxies that are undergoing a collision with another galaxy. Although not extremely common at this epoch, such systems of galaxies have been detected and extensively studied during recent years. There are now considerable data available to suggest that these systems commonly experience increased star formation, this taking place most often in the nuclei of the disk galaxies, rather than in their spiral arms.