Kinematically Lopsided Spiral Galaxies
  Asymmetries in the distribution of light and neutral hydrogen are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in their kinematics. Two examples of kinematically lopsided galaxies are presented and discussed. The shape of the rotation curve --rising more steeply on one side of the galaxy than on the other-- is the signature of the kinematic lopsidedness. It is shown that kinematic lopsidedness may be related to lopsidedness in the potential, and that even a mild perturbation in the latter can produce significant kinematical effects. Probably at least half of all spiral galaxies are lopsided. 
R.A. Swaters, R.H.M. Schoenmakers, R. Sancisi and T. S. van Albada