Are "Bondi-Hoyle Wakes" detectable in clusters of galaxies?
  In clusters of galaxies, the reaction of the intracluster medium (ICM) to the motion of the co-existing galaxies in the cluster triggers the formation of unique features, which trace their position and motion. Galactic wakes, for example, are an apparent result of the ICM/galaxy interactions, and they constitute an important tool for deciphering the motion of the cluster galaxies. In this paper we investigate whether Bondi-Hoyle accretion can create galactic wakes by focusing the ICM behind moving galaxies. The solution of the equations that describe this physical problem provide us with observable quantities along the wake at any time of its lifetime. We also investigate which are the best environmental conditions for the detectability of such structures in the X-ray images of clusters of galaxies. We find that significant Bondi-Hoyle wakes can only be formed in low temperature clusters, and that they are more pronounced behind slow-moving, relatively massive galaxies. The scale length of these elongated structures is not very large: in the most favourable conditions a Bondi-Hoyle wake in a cluster at the redshift of z=0.05 is 12 arcsec long. However, the wake's X-ray emission is noticeably strong: the X-ray flux can reach ~30 times the flux of the surrounding medium. Such features will be easily detectable in Chandra's and XMM-Newton's X-ray images of nearby, relatively poor clusters of galaxies. 
Irini Sakelliou (MSSL/UCL)