Polar-Ring Galaxies

Brad Whitmore and I have done some work on polar-ring galaxies, like this one, A0136-0801. Polar-ring galaxies are called that because their disks are aligned with the short axis of their central bulges, generally perpendicular to their long axis. The dynamically interesting feature they have is that their disk then samples the graviational potential in the polar plane of the bulge, rather than the equitorial like practically all other galaxies. Comparing velocities of the disk (or ring) to the bulge velocities gives us a handle on the shape of the halo of the galaxy, assuming that's what dominates the gravitional potential. Our results indicate that most such halos are near-spherical, but we do not have a large sample. And Penny Sackett gets different results with the same data.

There are different types of PRGs. There are the ones I call the Saturn types.

And the floppy, sombrero type, like this one.

Even finding the little beggars is not straightforward. Apparent inclination plays an enormous role in being able to identify the silly things. In the diagram below, we start with an intrinsic polar ring shape, and just rotate it around. As you can see, some end up looking like barred spirals, some look like "theta" galaxies. We figure we'd miss about 30-40 per cent just because of unfortunate inclination.

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