2009A&A...502..427V

Based on a comparison of dynamical models with observations of the interstellar gas in 6 Virgo cluster spiral galaxies, a first complete ram pressure stripping time sequence has been established. The observational characteristics of the different stages of ram pressure stripping are presented. The dynamical models yield the 3D velocity vectors of the galaxies, peak ram pressures, and times to peak ram pressure. In the case of a smooth, static, and spherical intracluster medium, peak ram pressure occurs during the galaxy's closest approach to the cluster center, i.e. when the galaxy's velocity vector is perpendicular to its distance vector from the cluster center (M87). Assuming this condition, the galaxy's present line-of-sight distance and its 3D position during peak ram pressure can be calculated. The linear orbital segments derived in this way, together with the intracluster medium density distribution derived from X-ray observations, give estimates of the ram pressure that are on average a factor of 2 higher than derived from the dynamical simulations for NGC 4501, NGC 4330, and NGC 4569. Resolving this discrepancy would require either a 2 times higher intracluster medium density than derived from X-ray observations, or a 2 times higher stripping efficiency than assumed by the dynamical models. Compared to NGC 4501, NGC 4330, and NGC 4569, NGC 4388 requires a still 2 times higher local intracluster medium density or a direction which is moderately different from that derived from the dynamical model. A possible scenario is presented for the dynamical evolution of NGC 4438 and M 86 within the Virgo cluster.