Warps are ubiquitious in Disc galaxies. Half of the observed Disc galaxies have warps in them. In fact all galaxies that could be observed to have warps have warps. However yet there is no satisfying answer exists to explain the existence of these warps. If one invokes magnetic fields to explain them it appears one needs values of fields too high to be acceptable. One explanation that has been popular was to have them as results of a misalignment between the equatorial plane of a Disc and a flattened Halo. This means the trivial (and only) discrete mode of a realistic Disc (with a smooth cut off to the density), a tilt with respect to some fiducial plane, changes into a warp mode. However the problem with this solution was the hypothesis of the static Halo. If one allowed the Halo to dynamically evolve and react to the changing Disc then it appears that the Disc settles down to the equatorial plane quickly. Even if one raises questions about vertical heating and the relative masses of the Disc and Halo in the numerical simulation of a self consistent Disc/Halo system, there still exists the original problem of where the initial misalignment may have arisen from.
Another possibility that has been raised as a possible origin for these warps is mass infall in galaxy that is expected in any model of formation of galaxies that involve hierarchical formation of structure. As mass shells collapse slight offsets from non-concentricity can cause mutual torques that can result in a smoothly changing orientation of the angular momentum of the final (not yet virialised) Halo of the galaxies. This will naturally lead to a torqueing of the Disc, and continual feeding of the torque by more and more material falling into the Halo can maintain a warp in the Disc.
Galaxies appear to have a density profile that is forever increasing with decreasing radius with no sign of dropping to uniform density. If the galaxies possess a bar with a definite pattern speed then the orbits in this potential will be scattered by the central density concetration if the orbits have a reduced waist in the rotating frame that they pass through near the center. It is also interesting to study the evolution of orbits in a bar under the influence of another bar with a different pattern speed and strength. Several galaxies including NGC 1291 and NGC 1317 have been observed to have a smaller bar inside a bigger one that aren't orthogonal to each other.
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