2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/3903The galaxy pair NGC 5194/95 (M 51) is one of the closest and best known interacting systems. Despite its notoriety, however, many of its features are not well studied. Extending westward from NGC 5195 is a low surface brightness tidal tail, which can only be seen in deep broadband exposures. Our previous [O III] lambda 5007 planetary nebulae (PN) survey of M 51 recovered this tidal tail, and presented us with a opportunity to study the kinematics of a galaxy interaction in progress. We report the results of a spectroscopy survey of the PN, aimed at determining their kinematic properties. We then use these data to constrain new self-consistent numerical models of the system.2 pages, 2 figures. To be published in IAU Symposium 209, Planetary Nebulae. Paper also available at http://burro.astr.cwru.edu/johnf/m51_proc.psAstrophysicstext