Kinematic lopsidedness in spiral galaxies

Morphological asymmetries between the approaching and receding sides in both the stellar and neutral hydrogen distribution are often observed in spiral galaxies. Here, attention is drawn to the presence of large-scale asymmetries in the kinematics of the neutral hydrogen gas. An example of such a kinematically lopsided galaxy is 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.