Interstellar Gas Cycling Powered by Star Formation
Star formation in molecular clouds is a low efficiency process. The mean conversion efficiency of gas into stars is about 1 – 10%, but lower values are often derived. Star formation is followed by a rapid dispersion of the unprocessed material from the active region. As a result, a large mass flux from the cold molecular phase of the interstellar medium towards its more diffuse phases is produced. When stationary state is assumed, this imprints a cycle of the interstellar matter, powered by star formation and feeded by the disruption of molecular clouds. We suggest that the flow is dominated by condensation processes which in sequence bring the gas to the highest densities found in protostellar clumps : cooling processes and related instabilities drive heated gas to HI state followed by mechanical processes as collisions of HI clouds or gravitation inside individual molecular clouds. Simplifying assumptions upon the condensation rates of each process allow for the calculation of the mass distribution over these various phases. The model presented here is a dynamical version of the standard two phase model, and predicts a nonequilibrium -though stationary- continuous distribution of lukewarm gas.
KeywordsMass Distribution Mass Flux Star Formation Interstellar Medium Gravitational Collapse
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