d) Are the Polar Rings Warped or Straight?
The nature of the warps which are seen in many polar rings may also provide clues about the formation mechanism (e.g., see Lake and Norman, 1983). In addition, Sparke (1986) has argued that self-gravity can hold a polar ring together against the effects of differential precession. Detailed models have been constructed for the self-gravity model in a few cases. These provide reasonable fits to the observed warp (Sparke 1990).
Of the 12 cases of category A and B galaxies where a clear determination can be made (i.e., after eliminating the narrow-ringed systems), only four appear to be essentially straight. Four more appear to be shaped like an integral sign, with the two sides warping in opposite directions. Of these four, two appear to be more nearly aligned along the minor axis at small radii (i.e., "integral-inner" designation in Table 1), while two are better aligned with the minor axis at large radii. Most surprising is the fact that four systems appear to have banana-shaped warps, with both sides bending in the same direction. UGC 07576 is a good example of this type of warp. Spiral galaxies that are warped invariably show integral-shaped warps rather than banana-shaped warps.