THE SURVIVAL OF THE SAGITTARIUS DWARF GALAXY AND THE FLATNESS OF THE ROTATION CURVE OF THE GALAXY

How has the ''fluffy'' Sgr dwarf galaxy survived its 10-20 pericentric passages in the halo of the Milky Way for a Hubble time? The scenario that Sgr was deflected to its current orbit by the Magellanic Clouds after a rendezvous on the north Galactic pole 2-3 Gyr ago is examined. It is shown that the conditions of the collision fix both the sense o f circulation of Sgr and the Large Magellanic Cloud around the Galaxy and the slope of the Galactic rotation curve. The model argues that th e two orthogonal polar circles traced by a dozen or so Galactic halo d warf galaxies and globular clusters (Lh?C-SMC-Magellanic Stream-Draco- Ursa Minor along l approximate to 270 degrees and M54-Ter 7-Ter 8-Arp 2-NGC 2419-Pal 15 along l approximate to 0 degrees) are streams of tid al relies from two ancient galaxies that were captured on two intersec ting polar rosette orbits by the Galaxy. Our results favor the interpr etation of microlensing toward the LMC being due to source or lens sta rs in tidal features of the Magellanic Clouds. We discuss direct and i ndirect observations to test the collision scenario.