Gasdynamics in interacting and merging galaxies

A three-dimensional model is developed for gas clouds orbiting in the gravitational potential of a galaxy which, at some later time, is perturbed by the gravitational influence of another galaxy. As the strength of the interaction increases, the interstellar medium becomes more disturbed. The clouds collide at an increased rate and with larger velocities, so that the fraction of collisions which disrupt the clouds rises rapidly as the strength of the interaction increases. On the other hand, no large increases in the rate at which massive clouds are built up are found. Since interacting galaxies are observed to have star formation efficiencies which are about five times higher than those in isolated galaxies, it is concluded that the star formation induced by the interaction of two galaxies is related to the high-velocity, disruptive cloud-cloud collisions. 46 refs.