The Sagittarius Dwarf Galaxy as a Product of Tidal Stirring

Abstract

We present a model of the nearby Sagittarius (Sgr) dwarf galaxy that correctly reproduces its present highly elongated shape. The model is based on an N-body simulation of a dwarf galaxy orbiting the Milky Way on an eccentric, tight orbit. The dwarf galaxy is initially composed of a stellar disk embedded in a dark matter halo. Strong tidal forces acting on the dwarf induce bar instability in the disk at the first pericenter passage. The bar is preserved until after the second pericenter which we identify as corresponding to the present time. The simulated dwarf, when observed from the Sun, shows remarkable similarity to the real distribution of M giant stars in Sgr. According to the model, the Sgr dwarf could not have spent much more than 1.3 Gyr on its present orbit or its stellar component would have already transformed into a perfectly spherical shape.