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

We show that collisions between the outer Galactic H i disk and the leading arms (LAs) of the Magellanic stream (MS) can create giant H i holes and chimneylike 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 H i 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 H i disk about 0.2 Gyr ago. We also find that the Magellanic impact can push out some fraction (∼ 1%) of the outer Galactic H i disk to form 1-10 kpc-scale H i holes and chimney-like bridges between the LAs and the disk. Subject headings: Magellanic Clouds – galaxies:structure – galaxies:kinematics and dynamics – galaxies:halos School of Physics, University of New South Wales, Sydney 2052, Australia, [email protected] Astronomical Institute, Tohoku University, Sendai, 980-8578, Japan, [email protected] Australia Telescope National Facility, CSIRO, P.O. Box 76, Epping NSW 1710, Australia, [email protected]