Head-On Collisions of Isothermal Clouds

Abstract

Using our three-dimensional hydrodynamics code BTSPH (Binary Tree SPH; Kim et al. 1994), we have simulated the head-on collisions between two identical clouds with 8000 particles. As an initial cloud we take an isothermal polytropic sphere in hydrostatic equilibrium with an external medium. Following Nagasawa & Miyama (1987) we characterize the initial cloud by parameter A defined as A = (36π/125)[G³M²/c⁸ _s]P _ext, where M is the cloud mass, c _s means the isothermal sound speed and P _ext represents the external pressure. The collision conditions are fully described by the parameter A and the relative collision Mach number defined as M _rel ≡ u _rel/c _s with u _rel being the relative velocity of the two clouds. We have examined the collision outcomes for total 45 combinations of A and M _rel.