BAR DISK ANGULAR-MOMENTUM EXCHANGE

We use a model galaxy with an artificial bar to explore the angular momentum exchange induced by bar-like (m = 2) perturbations to a disc. We provide an analytic formula for this exchange which predicts to within approximately 1 per cent the interaction between a weak bar and a non-self-gravitating disc. We also present the results of N-body experiments which suggest that the neglect of disc self-gravity in analytic theory leads to: (i) an underestimate of the slowdown rate of a bar which is dominated by corotation and outer Lindblad resonances; (ii) an overestimate of the spin-up rate of a bar which is dominated by inner Lindblad resonances. Additional simulations suggest that the importance of disc self-gravity is generally enhanced by increasing the age of the bar, but is lessened by increasing the temperature of the disc. All these effects have natural explanations, and estimates of their magnitude are provided for several particular cases.