Origin of Galactic Warps^*

Astronomisches Rechen-Institut, Mönchhofstrasse 12-14, 69120 Heidelberg, Germany and SGI Japan Ltd., 668-3, Moto-zaimoku-cho, Fushimi-ku, Kyoto 612-8043, Japan

Abstract

The origin of galactic warps is a long standing mystery. There has been progress recently in the theoretical understanding of the generation of warps, drawn from a reanalysis of the influence of a companion to a disc galaxy. A prominent example is found in the Milky Way - the LMC systems. Shortly after the discovery of the Milky Way's warp, it was shown that the direct torque from the LMC is too small to generate the observed warp in amount. We have performed numerical simulations in order to examine the effect of a live halo, as a mediator of the tidal interaction between the companion and the disc. We find with fairly realistic Milky Way models that the orbiting motion of the LMC excites massive wakes in the DM halo, and that these wakes produce larger torques on the disc than the companion alone. As a result the disc may develop a warp, of amplitude comparable to the one observed.