Publication Date:
2015-08-08
Description:
We investigate the abundance of galactic molecular hydrogen (H 2 ) in the ‘Evolution and Assembly of GaLaxies and their Environments’ (EAGLE) cosmological hydrodynamic simulations. We assign H 2 masses to gas particles in the simulations in post-processing using two different prescriptions that depend on the local dust-to-gas ratio and the interstellar radiation field. Both result in H 2 galaxy mass functions that agree well with observations in the local and high-redshift Universe. The simulations reproduce the observed scaling relations between the mass of H 2 and the stellar mass, star formation rate and stellar surface density. Towards high redshifts, galaxies in the simulations display larger H 2 mass fractions and lower H 2 depletion time-scales, also in good agreement with observations. The comoving mass density of H 2 in units of the critical density, $\Omega _{\rm H_2}$ , peaks at z 1.2–1.5, later than the predicted peak of the cosmic star formation rate activity, at z 2. This difference stems from the decrease in gas metallicity and increase in interstellar radiation field with redshift, both of which hamper H 2 formation. We find that the cosmic H 2 budget is dominated by galaxies with $M_{\rm H_2} 〉 10^9\,\rm M_{{\odot }}$ , star formation rates $ 〉 \,\!\!10\,\rm M_{{\odot }}\,\rm yr^{-1}$ and stellar masses M stellar 〉 10 10 M , which are readily observable in the optical and near-IR. The match between the H 2 properties of galaxies that emerge in the simulations and observations is remarkable, particularly since H 2 observations were not used to adjust parameters in EAGLE.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
Permalink
