Corrugations in galactic discs generated by Magellanic-type perturbers

Abstract

The small perpendicular distortions in a large disc galaxy, such as the Milky Walong-termy, that are caused by an orbiting intermediate-mass companion such as the Large Magellanic Cloud (LMC) have been modelled with a parallel computer implementation of a three-dimensinal N-body particle treecode. The model demonstrates that a companion with a mass fraction of 7.5 per cent of the Galaxy and an orbital inclination of 45° can generate height and perpendicular velocity perturbations of the inner disc of the primary galaxy that are of the order of several hundred pc and ∼ 10 km s-1, respectively, relative to an unperturbed system. The companion generates a spiral-shaped wave of perpendicular motions in the galactic disc which propagates from the edge inwards towards the bulge and forms a long-term, evolving spiral warp. The companion also significantly deforms the dark matter halo surrounding the Galaxy. The small perpendicular motions generated by the companion may account for some of the vertical deformations or corrugations that are observed in the Milky Way gas disc and for the slightly elevated velocity dispersions of the gas in some weakly interacting face-on galaxies. ©1997 RAS.