ENERGY-DISSIPATION IN INTERSTELLAR CLOUD COLLISIONS

We present a study of the kinetic energy dissipation in interstellar c loud collisions. The main aim is to understand the dependence of the e lasticity (defined as the ratio of the final to the initial kinetic en ergy of the clouds) on the velocity and mass ratio of the colliding cl ouds, magnetic field strength, and gas metallicity for head-on collisi ons. The problem has been studied both analytically and via numerical simulations. We have derived handy analytical relationships that well approximate the analogous numerical results. The main findings of this work are the following: (1) the kinetic energy dissipation in cloud c ollisions is minimum (i.e., the collision elasticity is maximum) for a cloud relative velocity upsilon(r) similar or equal to 30 km s(-1) (2 ) the above minimum value is proportional ZL(c)(2), where Z is the met allicity and L-c is the cloud size (the larger ZL(c)(2) is, the more d issipative, i.e., inelastic, the collision will be); and (3) in genera l, we find that the energy dissipation decreases when the magnetic fie ld strength and mass ratio of the clouds are increased and the metalli city is decreased respectively. We briefly discuss the relevance of th is study to the global structure of the interstellar medium and to gal axy formation and evolution.