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Three-dimensional episodic model of star formation in galaxies in the presence of dissipation


 The oscillatory model of star formation in giant and dwarf galaxies have been studied through a dynamical open system. In addition to various dynamical processes involving fractional masses of hot, warm, and cold gases, the system is subjected to dissipative processes e.g. outflow from the gaseous component caused by supernovae explosion and subsequent ram pressure stripping within the oscillation period. This is more realistic than a previous model which was considered conservative. The present episodic model has been found to be unimodal in general contrary to discrete episodes of star formation of decreasing amplitudes as found for closed systems. The duty cycles under various parametric conditions derived, vary in the range (2.0–40.0) × 107 yr for giant galaxies contrary to longer time, for example 9.0 × 107–1.0 × 109 yr for dwarf galaxies. This might be due to the low production rate of supernova in dwarf galaxies which reduces the evaporation rate of cold gas into hot gas making cold gas available for continuing the cycle for a longer time. The duty cycles have increased in both cases compared to the previous model by an order of one for giant galaxies and order of two for dwarf galaxies depending on the degree of dissipation. This might be due to the unimodal pattern of star formation which prevails for longer time in the late phase of galaxy evolution. Under very special parametric conditions limit cycles may occur i.e. star formation in discrete episodes, may occur involving one or more stable attractors especially in early-type dwarf and giant galaxies. Tendency of formation of multiple attractors are more likely in early-type giant spiral galaxies when the rate of dissipation is very slow.