Ram pressure stripping of disk galaxies
Galaxies exist in various environments, ranging from isolated field galaxies over galaxy groups to clusters. In addition to galaxies, clusters and groups are filled with a hot tenuous gas, the intracluster medium or intragroup medium (abbreviated ICM for both). Comparative observations of galaxies, especially disk galaxies, in various environments reveal systematic differences in morphology, colour, star formation activity and gas contents. Theoretical work has proposed several mechanisms that can be at work in clusters and groups. On the one hand there are (gravitational) interactions among the galaxies themselves, on the other hand there is the interaction between the galaxies and the ICM. The basic idea for the latter is that a galaxy is stripped of its gas by ram pressure as it moves through the ICM. The gas is the raw material for star formation, therefore such ram pressure stripping (RPS) has severe consequences for a galaxy. The aim of this work is to study the process of RPS of disk galaxies with hydrodynamical simulations. The simulations in this work are restricted to the face-on case, which allows us to use a 2D code. This enables us to use high resolution and to compile a comprehensive parameter study that varies galaxy properties as well as ICM conditions. We find that RPS proceeds in three phases: firstly the instantaneous stripping phase, secondly the dynamic intermediate phase, and thirdly the quasi-stable continuous viscous stripping phase. The stripping efficiency depends slightly on the Mach number of the ICM flow, however, the main parameter is the ram pressure. For a fixed galactic gas surface density the stripping efficiency does not depend on the vertical structure and thickness of the gas disk. The numerical results for the stripping efficiency are in good agreement with analytical estimates. From our simulations we conclude that gas disks of galaxies in high density environments (like cluster centres) are heavily truncated or even completely stripped. But also the gas disks of galaxies in low density environments (cluster outskirts or groups) are disturbed by the ICM-flow and back-falling material, so that they should also be pre-processed.