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The tidal stirring model envisions the formation of dwarf spheroidal (dSph)galaxies in the Local Group via the tidal interaction of disky dwarf systemswith a larger host galaxy like the Milky Way. These progenitor disks areembedded in extended dark halos and during the evolution both components sufferstrong mass loss. In addition, the disks undergo the morphologicaltransformation into spheroids and the transition from ordered to random motionof their stars. Using collisionless N-body simulations we construct a model forthe nearby and highly elongated Sagittarius (Sgr) dSph galaxy within theframework of the tidal stirring scenario. Constrained by the present knownorbit of the dwarf, the model suggests that in order to produce the majority oftidal debris observed as the Sgr stream, but not yet transform the core of thedwarf into a spherical shape, Sgr must have just passed the second pericenterof its current orbit around the Milky Way. In the model, the stellar componentof Sgr is still very elongated after the second pericenter and morphologicallyintermediate between the strong bar formed at the first pericenter and thealmost spherical shape existing after the third pericenter. This is thus thefirst model of the evolution of the Sgr dwarf that accounts for its observedvery elliptical shape. At the present time there is very little intrinsicrotation left and the velocity gradient detected along the major axis is almostentirely of tidal origin. We model the recently measured velocity dispersionprofile for Sgr assuming that mass traces light and estimate its current totalmass within 5 kpc to be 5.2 x 10^8 M_sun. To have this mass at present, themodel requires that the initial virial mass of Sgr must have been as high as1.6 x 10^10 M_sun, comparable to that of the Large Magellanic Cloud, which mayserve as a suitable analog for the pre-interaction, Sgr progenitor.

The inner structure and kinematics of the Sagittarius dwarf galaxy as a product of tidal stirring