Abstract
ABSTRACT The reservoir of molecular gas (H2) represents the fuel for the star formation (SF) of a galaxy. Connecting the star formation rate (SFR) to the available H2 is key to accurately model SF in cosmological simulations of galaxy formation. We investigate how modifying the underlying modelling of H2 and the description of stellar feedback in low-metallicity environments (LMF, i.e. low-metallicity stellar feedback) in cosmological zoomed-in simulations of a Milky Way-size halo influences the formation history of the forming, spiral galaxy, and its final properties. We exploit two different models to compute the molecular fraction of cold gas ($f_{\rm H_{2}}$): (i) the theoretical model by Krumholz et al. (2009b) and (ii) the phenomenological prescription by Blitz and Rosolowsky (2006). We find that the model adopted to estimate $f_{\rm H_{2}}$ plays a key role in determining final properties and in shaping the morphology of the galaxy. The clumpier interstellar medium (ISM) and the more complex H2 distribution that the Krumholz et al. model predicts result in better agreement with observations of nearby disc galaxies. This shows how crucial it is to link the SFR to the physical properties of the star-forming, molecular ISM. The additional source of energy that LMF supplies in a metal-poor ISM is key in controlling SF at high redshift and in regulating the reservoir of SF across cosmic time. Not only is LMF able to regulate cooling properties of the ISM, but it also reduces the stellar mass of the galaxy bulge. These findings can foster the improvement of the numerical modelling of SF in cosmological simulations.
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