  Rotation curves of interacting galaxies often show that velocities are either
rising or falling in the direction of the companion galaxy. We seek to
reproduce and analyse these features in the rotation curves of simulated
equal-mass galaxies suffering a one-to-one encounter, as possible indicators of
close encounters. Using simulations of major mergers in 3D, we study the time
evolution of these asymmetries in a pair of galaxies, during the first passage.
Our main results are: (a) the rotation curve asymmetries appear right at
pericentre of the first passage, (b) the significant disturbed rotation
velocities occur within a small time interval, of ~ 0.5 Gyr h^-1, and therefore
the presence of bifurcation in the velocity curve could be used as an indicator
of the pericentre occurrence. These results are in qualitative agreement with
previous findings for minor mergers and fly-byes.
