Archer of the galactic disk? The effect on the outer H I disk of the Milky Way of collisional encounters with the Sagittarius dwarf galaxy

Hydrodynamical calculations undertaken to simulate the collisional interaction between the Sagittarius dwarf and the Galactic outer H I disk are presented, constrained by recently derived orbital and mass parameters for this dwarf galaxy. It is found that a significant distortion to the structure of the Galactic H I disk will be induced by the collision if the mass of the dwarf exceeds similar to 10(9) M.; this value is consistent with an estimate derived by requiring that the dwarf galaxy is sufficiently robust to survive tidal disruption until the present time. Though the precise details of the interaction are compromised in our simulations by the lack of a live Galactic halo, we find that for model masses greater than or similar to 5 x 10(9) M., prominent spiral arms and a substantial lopsidedness in the outer disk are produced. Furthermore, a noticeable warp-like structure is induced in the disk. Thus the Sagittarius dwarf may have significantly affected the star formation history and structure of the outer Galaxy. These simulations confirm the possibility of determining the current merging rate of low surface brightness, gas-poor dwarf galaxies of mass greater than or similar to 10(9) M. onto giant spiral galaxies from careful analysis of observations of the structure of H I disks.