Warping of disk galaxies. I. Theory

We show that if spiral galaxies formed with two inclinded disks, warps in spiral galaxies are a natural result of the disks' interactions. The precession of gas clouds and their subsequent inelastic collisions determine the shape and extent of the warp. There is good agreement with the results of an analytic model and numerical experiments compared to the warps in our Galaxy and M31. A brief argument is given showing the plausibility of galaxies forming with two inclined disks