A hybrid N-body/cellular automaton scheme for modelling propagating star formation in galaxies

We present a numerical scheme for modelling star formation in galaxies based on the dual operation of gravitational instabilities and propagating star formation. Star formation is superposed on a mechanical N-body simulation of a collisional particle system by using a cellular automaton framework. The simulations involve 5000 particles representing gas clouds which can collide inelastically, and have been performed on a 2D square surface with quasiperiodic boundary conditions. The input of kinetic energy from star-forming regions leads to self-regulation of the global dynamics of star formation. The model naturally generates cloud complexes assembled from groups of cloud particles and simulates the ignition and propagation of star formation in such complexes leading to the formation of low density bubbles and expanding shells. The percentage of the model surface undergoing star formation and the ratio of the rates of stimulated to spontaneous star formation are shown to be consistent with models based on the theory of Stochastic Self-Propagating Star Formation (SSPSF). The code is shown to lead to star formation that propagates very nearly isotropically and can thus be adapted to the case of rotating disc galaxies without geometrical modification.