# Molecular hydrogen abundances of galaxies in the EAGLE simulations

Lagos, CDP, Crain, RA, Schaye, J, Furlong, M, Frenk, CS, Bower, RG, Schaller, M, Theuns, T, Trayford, JW, Bahe, YM and Vecchia, CD (2015) Molecular hydrogen abundances of galaxies in the EAGLE simulations. Monthly Notices of the Royal Astronomical Society, 452 (4). pp. 3815-3837. ISSN 0035-8711

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## Abstract

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 edshifts, galaxies in the simulations display larger H$_2$ mass fractions, and correspondingly lower H$_2$ depletion timescales, 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 $z\approx 1.2-1.5$, later than the predicted peak of the cosmic star formation rate activity, at $z\approx 2$. 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 $M_{\rm stellar}>10^{10}\,\rm M_{\odot}$, 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 it involves no adjustable parameters.

Item Type: Article This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of recordMNRAS (October 01, 2015) 452 (4): 3815-3837 is available online at: http://dx.doi.org/10.1093/mnras/stv1488 astro-ph.GA; astro-ph.GA; astro-ph.CO Q Science > QB Astronomy Astrophysics Research Institute Oxford University Press Author 25 Mar 2015 11:57 04 Sep 2021 14:33 https://researchonline.ljmu.ac.uk/id/eprint/813

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