ORBITS OF THE MAGELLANIC CLOUDS AND LEO-I IN LOCAL GROUP HISTORY

The Magellanic Clouds and Leo I present several problems when they are interpreted as systems that have been permanently bound to the Milky Way since formation together in the Big Bang. The large angular momentum of the Magellanic Clouds relative to the Milky Way and the exceptionally large radial velocity of Leo I suggest that these satellites should be considered in the wider context of the whole Local Group. We use as observational constraints recently measured proper motions, distances, and radial velocities of these satellites. We also use previous estimates of the star formation history of the Milky Way, an age of the universe of about 15 billion years and the tidal radius of Leo I. We calculated backwards the orbits of LMC/SMC (treated as a single unit) along with Leo I assuming different values for unknown or uncertain parameters such as the mass of the galaxy. In the simulations consistent with the observational constraints, both the Magellanic Clouds and Leo I seem to have left the neighborhood of the Andromeda Galaxy about 10 billion years ago explaining the angular momentum and radial velocity problems. In these simulations, the mass of our galaxy is about 10(12) M..