Origin of Galactic Warps^*

Abstract

The origin of galactic warps is a long standing mystery. There has beenprogress recently in the theoretical understanding of thegeneration 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 thatthe direct torque from the LMC is too small to generate the observedwarp in amount. We have performed numerical simulations in order to examinethe effect of a live halo, as a mediator of the tidal interaction betweenthe companion and the disc. We find with fairly realistic MilkyWay models that the orbiting motion of the LMC excites massive wakesin 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.