Galaxies in Clusters: the Observational Characteristics of Bow-Shocks, Wakes and Tails

Abstract

The dynamical signatures of the interaction between galaxies in clusters and the intracluster medium (ICM) can potentially yield significant information about the structure and dynamical history of clusters. To develop our understanding of this phenomenon we present results from numerical modelling of the galaxy/ICM interaction, as the galaxy moves through the cluster. The simulations have been performed for a broad range, of ICM temperatures (kT = 1,4 and 8 keV), representative of poor clusters or groups through to rich clusters. There are several dynamical features that can be identified in these simulations; for supersonic galaxy motion, a leading bow-shock is present, and also a weak gravitationally focussed wake or tail behind the galaxy (analogous to Bondi-Hoyle accretion). For galaxies with higher mass-replenishment rates and a denser interstellar medium (ISM), the dominant feature is a dense ram-pressure stripped tail. In line with other simulations, we find that the ICM/galaxy ISM interaction can result in complex time- dependent dynamics, with ram-pressure stripping occurring in an episodic manner. In order to facilitate this comparison between the observational consequences of dynamical studies and X-ray observations we have calculated synthetic X-ray flux and hardness maps from these simulations. These calculations predict that the ram-pressure stripped tail will usually be the most visible feature, though in nearby galaxies the bow-shock preceding the galaxy should also be apparent in deeper X-ray observations. We briefly discuss these results and compare with X-ray observations of galaxies where there is evidence of such interactions.