The Development of Gas/Star Offsets in Tidal Tails
  We present models of interacting galaxies in order to study the development of spatial offsets between the gaseous and stellar components in tidal tails. Observationally, such offsets are observed to exist over large scales (e.g., NGC 3690; Hibbard et al. 2000), suggesting an interaction between the tidal gas and some (unseen) hot ISM. Instead, our models show these offsets are a natural consequence of the radially extended HI spatial distribution in disk galaxies, coupled with internal dissipation in the gaseous component driven by the interaction. This mechanism is most effective in systems involved in very prograde interactions, and explains the observed gas/star offsets in interacting galaxies without invoking interactions with a hot ISM, starburst ionization, or dust obscuration within the tails. 
Chris Mihos (Case Western Reserve University)