The effects of metallicity, UV radiation and non-equilibrium chemistry in high-resolution simulations of galaxies

Richings, A. J.; Schaye, Joop

Abstract

We present a series of hydrodynamic simulations of isolated galaxies with stellar mass of 109M˙. The models use a resolution of 750M˙ per particle and include a treatment for the full non-equilibrium chemical evolution of ions and molecules (157 species in total), along with gas cooling rates computed self-consistently using the non-equilibrium abundances. We compare these to simulations evolved using cooling rates calculated assuming chemical (including ionization) equilibrium, and we consider a wide range of metallicities and UV radiation fields, including a local prescription for self-shielding by gas and dust.We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool to a cold (few hundred Kelvin) star-forming phase under such conditions. Contrary to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties. However, it is important for modelling molecular outflows. For example, the mass of H2 outflowing with velocities > 50 km s-1 is enhanced by a factor ~20 in non-equilibrium. We also compute the observable line emission from C II and CO. Both are stronger at higher metallicity, while C II and CO emission are higher for stronger and weaker radiation fields, respectively. We find that C II is generally unaffected by non-equilibrium chemistry. However, emission from CO varies by a factor of ~2-4. This has implications for the mean XCO conversion factor between CO emission and H2 column density, which we find is lowered by up to a factor ~2.3 in non-equilibrium, and for the fraction of CO-dark molecular gas.

Citation

Richings, A. J., & Schaye, J. (2016). The effects of metallicity, UV radiation and non-equilibrium chemistry in high-resolution simulations of galaxies. Monthly notices of the Royal Astronomical Society, 458(1), 270-292. https://doi.org/10.1093/mnras/stw327

• Journal Article Type: Article
• Acceptance Date: Feb 9, 2016
• Online Publication Date: Feb 11, 2016
• Publication Date: Feb 22, 2016
• Deposit Date: Aug 23, 2023
• Publicly Available Date: Oct 13, 2023
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 458
• Issue: 1
• Pages: 270-292
• DOI: https://doi.org/10.1093/mnras/stw327
• Public URL: https://hull-repository.worktribe.com/output/4132566
• Publisher URL: https://academic.oup.com/mnras/article/458/1/270/2622556?login=false