Contribution of the Large Magellanic Cloud to the Galactic Warp

Abstract

Multi-scale interaction between the LMC, Galactic halo, and the disk is examined with N-body simulations, and precise amplitudes of the Galactic warp excitation are obtained. The Galactic models are constructed most realistically to satisfy available observational constraints on the local circular velocity, the mass, surface density and thickness of the disk, the mass and size of the bulge, the local density of the halo matter at the solar radius, and the mass and orbit of the LMC. By using hybrid algorithm (SCF-TREE) I have succeeded to follow the evolution with millions of particles. The orbiting satellite excites density enhancement as a wake, and the wake exerts a tidal force on the disk. Because of the additional torque from the wakes in the halo, the amplitudes of the induced warps are much larger than the classical estimate by [hunt1969], who considered only the direct torque from the LMC. The obtained amplitudes of m=0, 1, 2 warps in the larger halo model show very good agreement with the observed amplitude in the Milky Way. This result revives the LMC as a possible candidate of the origin of the Galactic warp. Our smaller halo model, however, yield only weak warps in all the harmonic modes. Therefore the halo still has significant influence on excitation of warp even in the interaction scenario for excitation of warps.