9320403 Sparke Galaxies are widely believed to have unseen 'dark' halos containing much of the mass of the system. The halo is more extended than the luminous material, and its mass distribution is best probed by studying the outermost orbits of stars and gas. Models for warped disks in spiral galaxies, and for polar rings around SO galaxies, show that these can be understood as self- gravitating structures in the potential of the massive halo. The form expected for the warp or the polar ring, and velocities of orbits within these structures, depend on how mass is distributed within the unseen halo: on the central concentration, on the flattening normal to the disk plane, on whether it is significantly triaxial. Support will be provided both for theoretical modeling and observations. Theoretical work on warps will address the effect of a galactic bulge, warps with different azimuthal dependences, and the eventual damping of warps due to interaction with the halo. Optical and HI observations of warped systems will also be made. Dynamical modeling of polar rings will concentrate on the effect of triaxiality, and on detailed models for particular observed systems to establish parameters; the observational program includes high-resolution HI mapping of the rings, radio surveys, and optical imaging and spectroscopy
