Unexpected behaviour in the rotation of perturbed barred galaxies

Computer simulations of perturbations of barred galaxies show that the rotational velocity of the bar can be increased or decreased by the perturbation. Earlier investigations propose that the perturbed bar would increase its rotational velocity for positive torques and respectively decrease the rotation speed for negative torques (Gerin et al. 1990). This Letter shows that such a behaviour is not generally true. The result will depend on the mass of the perturber and the angle between the bar and the perturber at its closest passage. The parameter space consisting of these variables is investigated in this Letter, showing a unexpected behaviour of the bar upon perturbation.