Magellanic Clouds and LeoI's Orbits in Local Group History

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Session 108 -- Dwarf and Irregular Galaxies
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[108.08] Magellanic Clouds and LeoI's Orbits in Local Group History

Gene Byrd (University of Alabama, Tuscaloosa), Mauri Valtonen (Tuorla Observatory, Finland), Marshall McCall, Kimmo Innanen (York University, Canada)

The large angular momentum of the Magellanic Clouds and the exceptionally large radial velocity of Leo I relative to the Milky Way suggest that their history should be considered in the context of the whole Local Group rather than as always being bound to the Galaxy. As observational constraints we use: the Magellanic Clouds' proper motions, the distances and radial velocities of both satellites, the star formation history of the Milky Way, the age of the universe and the tidal radius of Leo I. We calculated backwards the orbits of the Magellanic Clouds and Leo I assuming different values for unknown or uncertain parameters such as the mass of the Galaxy ($\sim\,10^{12} \,M_{\odot}$). In simulations consistent with these constraints, both the Magellanic Clouds and Leo I seem to have left the neighborhood of M31 about 10 billion years ago explaining their large angular momentum and radial velocity. In contrast to Leo I, the Magellanic Clouds have been captured into a bound orbit around our galaxy via dynamical friction. The Clouds are presently having their second close passage. Simulation plots of the orbits of these satellites and major galaxies in the Local Group since the Big Bang will be shown.

This work was supported by the Finnish Academy, NSF EPSCoR RII8996152 and NSF AST 9014137 (GB).

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