A comparison of $\text{H}_2$ formation models at high redshift

Alexander Schäbe; Emilio Romano-Díaz; Cristiano Porciani; Aaron D. Ludlow; Matteo Tomassetti

doi:10.1093/mnras/staa2313

paper

A comparison of $H_{2}$ formation models at high redshift

arXiv:2003.04329 · doi:10.1093/mnras/staa2313

Abstract

Modelling the molecular gas that is routinely detected through CO observations of high-redshift galaxies constitutes a major challenge for ab initio simulations of galaxy formation. We carry out a suite of cosmological hydrodynamic simulations to compare three approximate methods that have been used in the literature to track the formation and evolution of the simplest and most abundant molecule, H $_{2}$ . Namely, we consider: i) a semi-empirical procedure that associates H $_{2}$ to dark-matter haloes based on a series of scaling relations inferred from observations, ii) a model that assumes chemical equilibrium between the H $_{2}$ formation and destruction rates, and iii) a model that fully solves the out-of-equilibrium rate equations and accounts for the unresolved structure of molecular clouds. We study the impact of finite spatial resolution and show that robust H $_{2}$ masses at redshift $z \approx 4$ can only be obtained for galaxies that are sufficiently metal enriched in which H $_{2}$ formation is fast. This corresponds to H $_{2}$ reservoirs with masses $M_{H_{2}} ≳ 6 \times 1 0^{9} M_{⊙}$ . In this range, equilibrium and non-equilibrium models predict similar molecular masses (but different galaxy morphologies) while the semi-empirical method produces less H $_{2}$ . The star formation rates as well as the stellar and H $_{2}$ masses of the simulated galaxies are in line with those observed in actual galaxies at similar redshifts that are not massive starbursts. The H $_{2}$ mass functions extracted from the simulations at $z \approx 4$ agree well with recent observations that only sample the high-mass end. However, our results indicate that most molecular material at high $z$ lies yet undetected in reservoirs with $1 0^{9} < M_{H_{2}} < 1 0^{10} M_{⊙}$ .

arXiv comment19 pages, 12 figures, 1 table, accepted for publication in MNRAS, comments are welcome

A comparison of $H_{2}$ formation models at high redshift

Abstract

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A comparison of H2​ formation models at high redshift

Abstract

References in corpus (121)

Cited by in corpus (6)

A comparison of $H_{2}$ formation models at high redshift