Incorporating the molecular gas phase in galaxy-size numerical simulations: first applications in dwarf galaxies
Abstract
We present models of the evolution of the gaseous and stellar content of galaxies incorporating the formation of H2 out of HI gas as part of such a model. We do so by formulating a subgrid model for gas clouds that uses well-known cloud scaling relations and solves for the HI-H2 balance set by the H2 formation on dust grains and its FUV-induced photodissociation by the temporally and spatially varying interstellar radiation field. This allows the seamless tracking of the evolution of the H2 gas phase, its precursor Cold Neutral Medium (CNM) HI gas, simultaneously with the star formation. Our most important findings are: a) a significant dependence of the HI-H2 transition and the resultant H2 gas mass on the ambient metallicity and the H2 formation rate, b) the important influence of the characteristic star formation timescale (regulating the ambient FUV radiation field) on the equilibrium H2 gas mass and c) the possibility of a diffuse H2 gas phase. Finally, we implement and briefly explore a novel approach of using the ambient H2 gas mass fraction as a criterion for the onset of star formation. (abridged)
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