IAU Symposium Abstract S186-039T

The Making of Spirals with Counter-Rotating Disks
D. Pfenniger
Geneva Observatory, University of Geneva, CH-1290 Sauverny, Switzerland < daniel.pfenniger@obs.unige.ch >

We study a new merger scenario for making galaxies displaying today coplanar counter-rotating stellar disks, such as NGC 4550. From simple dynamical considerations we select out the most promising merger scenario, which is then quantitatively studied by N-body technique, either with a purely collisionless component, or with an substantial additional dissipative (gaseous) component. Observational cases also motivate this particular scenario, which might look a priori unlikely. Beside providing an explanation in term of merger event for the existence of counter-rotating disks, the scenario predicts that some spirals should have in appearance two bulges; from a limited search at least one case has been found.