SIMULATION OF THE INTERACTING TRIPLET M81, M82, NGC3077

M81 is clearly interacting with its two neighbouring galaxies M82 and NGC3077. First we simulated the deformation of the atomic gas in the triplet, using a straightforward model (restricted to the 3-body problem), in order to determine the parameters of the trajectories for the three galaxies. The resulting external tidal features satisfactorily resemble the observed HI bridges and tails. We then used a model of cloud collisions to simulate the response of the M81 molecular content. However the 3-body model parameters are not compatible with such a model. Stronger perturbations are needed in a self-consistent gas and stars simulation to produce and amplify a spiral density wave in the inner disk of M81. Preliminary tests show that a strong wave can be amplified both in the stars and gas components, the global structure bearing some resemblance with the observations. The model parameters must now be improved in the light of the most recent observational data.