Moment-1 H I velocity field of the six galaxies with a one-sided H I tail. The galaxy name is given at the top of each image. Below the galaxy name, we indicate the H I systemic velocity, which is represented by the thick white iso-velocity contour in the figure, as well as the levels of the other contours (n = 0, 1, …). The coloured frame around the contour levels indicates whether a galaxy is blue- or redshifted relative to NGC 1399, whose velocity is ∼1425 km s⁻¹. The bottom left black ellipse represents the 41″ H I resolution. The small open black circle represents the galaxy centre. The thin black contour is the first H I contour shown in Fig. 9.