Simulation of the Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies

TL;DR

This paper simulates the cosmic evolution of atomic and molecular hydrogen in galaxies using a large cosmological simulation, providing insights into gas properties and their evolution over cosmic time.

Contribution

It introduces a set of physical prescriptions to assign HI and H2 to galaxies in large simulations, enabling realistic modeling of gas properties and emission lines.

Findings

Reproduces local HI and H2 mass functions accurately.

Matches observed CO luminosity functions and Tully-Fisher relation.

Predicts significant evolution of gas properties at high redshift.

Abstract

We present a simulation of the cosmic evolution of the atomic and molecular phases of the cold hydrogen gas in about 3e7 galaxies, obtained by post-processing the virtual galaxy catalog produced by (De Lucia et al. 2007) on the Millennium Simulation of cosmic structure (Springel et al. 2005). Our method uses a set of physical prescriptions to assign neutral atomic hydrogen (HI) and molecular hydrogen (H2) to galaxies, based on their total cold gas masses and a few additional galaxy properties. These prescriptions are specially designed for large cosmological simulations, where, given current computational limitations, individual galaxies can only be represented by simplistic model-objects with a few global properties. Our recipes allow us to (i) split total cold gas masses between HI, H2, and Helium, (ii) assign realistic sizes to both the HI- and H2-disks, and (iii) evaluate the corresponding velocity profiles and shapes of the characteristic radio emission lines. The results presented in this paper include the local HI- and H2-mass functions, the CO-luminosity function, the cold gas mass--diameter relation, and the Tully-Fisher relation (TFR), which all match recent observational data from the local Universe. We also present high-redshift predictions of cold gas diameters and the TFR, both of which appear to evolve markedly with redshift.