Can Gas and Stars be Separated in a Tidal Interaction?

Abstract

A great deal of attention has been given in recent years to the dynamical behaviour of stars in tidal interactions between galaxies as inferred from computer models (e.g., Toomre and Toomre, 1972). However very little work has been done on the response of the gas component of a galaxy to strong tidal forces. Much of our observational data on the kinematics of galaxies are based on measurements of either neutral or ionised gas rather than stars. If meaningful dynamical information is to be extracted from the stellar models it is important to question whether the kinematics of the gas always approximately follows that of the stars in tidally interacting galaxies. Foster (in a companion paper in this volume) describes some preliminary attempts by the Manchester group to model gas in interacting galaxies. In this present paper I shall briefly report on some observations and a particle simulation which supports the view that gas dynamical effects may be important in some tidal encounters.