The Magellanic impact: Collision between the outer Galactic HI disk and the leading arms of the Magellanic stream

We show that collisions between the outer Galactic HI disk and the leading arms (LAs) of the Magellanic stream (MS) can create giant HI holes and chimney-like structures in the disk. Based on the results of our N-body simulations on the last 2.5 Gyr evolution of the Large and Small Magellanic Clouds (LMC and SMC, respectively) interacting with the Galaxy, we investigate when and where the LAs can pass through the Galactic plane after the MS formation. We then investigate hydrodynamical interaction between LAs and the Galactic HI disk (``the Magellanic impact'') by using our new hydrodynamical simulations with somewhat idealized models of the LAs. We find that about 1-3% of the initial gas mass of the SMC, which consists of the LAs, can pass through the outer part (R=20-35 kpc) of the Galactic HI disk about 0.2 Gyr ago. We also find that the Magellanic impact can push out some fraction (~1%) of the outer Galactic HI disk to form 1-10 kpc-scale HI holes and chimney-like bridges between the LAs and the disk.