Dynamic Equilibrium Sets of the Atomic Content of Galaxies across Cosmic Time

• Published in: The Astrophysical journal Vol. 868; no. 2; pp. 93 - 101
• Main Authors: Wang, Liang, Obreschkow, Danail, Lagos, Claudia D. P., Sweet, Sarah M., Fisher, Deanne B., Glazebrook, Karl, Macciò, Andrea V., Dutton, Aaron A., Kang, Xi
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.12.2018; IOP Publishing
• Subjects: Angular momentum; Astrophysics; Cold gas; Computer simulation; Deposition; Disk galaxies; Environmental effects; Equilibrium; Evolution; Galactic evolution; Galaxies; galaxies: dwarf; galaxies: evolution; galaxies: formation; galaxies: spiral; methods: numerical; Stability; Star & galaxy formation; Star formation; Stars & galaxies; Static equilibrium; Time
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aae8de

We analyze 88 independent, high-resolution, cosmological zoomed-in simulations of disk galaxies in the NIHAO simulations suite to explore the connection between the atomic gas fraction and angular momentum (AM) of baryons throughout cosmic time. The study is motivated by the analytical model of Obreschkow et al., which predicts a relation between the atomic gas fraction fatm and the integrated atomic stability parameter , where M and j are the mass and specific AM of the galaxy (stars+cold gas) and is the velocity dispersion of the atomic gas. We show that the simulated galaxies follow this relation from their formation (z 4) to the present within ∼0.5 dex. To explain this behavior, we explore the evolution of the local Toomre stability and find that 90%-100% of the atomic gas in all simulated galaxies is stable at any time. In other words, throughout the entire epoch of peak star formation until today, the timescale for accretion is longer than the timescale to reach equilibrium, thus resulting in a quasi-static equilibrium of atomic gas at any time. Hence, the evolution of fatm depends on the complex hierarchical growth history primarily via the evolution of q. An exception is galaxies subject to strong environmental effects.