Category A - Kinematically Confirmed (6 objects)
- Spectroscopic evidence must exist for two nearly orthogonal angular
momentum vectors with similar amplitudes.
- The system must be in an equilibrium or quasi-equilibrium
configuration, as shown by the fact that:
- - both components must have similar systemic velocities, and
- - the centers of the two components must be nearly aligned.
- The ring must be comparable in size to the inner component, must be
luminous (i.e., dust-lane ellipticals are not included), and it must
be nearly planar (i.e., the chaotic appearance of M82 would be ruled out).