A NEW MODEL FOR THE FORMATION OF KINEMATICALLY DECOUPLED CORES IN ELLIPTIC GALAXIES

We propose a new mechanism for the formation of elliptical galaxies wi th kinematically decoupled cores (KDCs), in which the decoupling arise s from an interaction event of an elliptical galaxy with an embedded d isc. In this scenario, a merger is not required, as the galaxy halo is kinematically decoupled from the core as the result of a flyby intera ction with another galaxy. We present the result of a test particle si mulation in which an elliptical galaxy with an embedded dsc is involve d in a retrograde flyby encounter with a secondary elliptical. The rot ation curve bears a strong resemblance to those of galaxies with KDCs, having a rapidly spinning core and st slowly rotating decoupled halo. We argue that systems like IC 1459, NGC 5322 and NGC 3656 are better explained by this model than by the merger of a small compact elliptic al.