Tidal Torques and Galactic Warps

Abstract

We investigate the tilting and warping of galactic disks in response to tidal torquing. The strength of the torque is determined from cosmological N-body simulations. We find the tidal torques to be dominated by substructure in the galactic halo, such as dwarf satellites, and by a misalignment between the disk angular momentum and the figure axes of the dark matter halo. The radial dependence of the torque can approximated by a power law of index -2.5. A massless disk subjected to such a torque develops a trailing warp similar to those seen in a large number of disk galaxies, i.e. the inner regions of the disk tilt faster than the outer disk. In the case of massive disks, self gravity causes the inner disk to stay locally flat and only the outer regions show the signatures of warps. The radius outside of which a massive disk is warped depends on the local surface density of the disk and on the product of the strength of the torque and the exposure time to this torque.