Molecular gas, CO, and star formation in galaxies: emergent empirical relations, feedback, and the evolution of very gas-rich systems

TL;DR

This paper uses advanced simulations to study how molecular gas and star formation relate in galaxies, revealing that empirical relations like the Kennicutt-Schmidt law emerge naturally after galaxies reach a dynamic equilibrium, especially in gas-rich systems.

Contribution

It introduces a time-varying model of galaxy evolution that incorporates CO formation and destruction, providing new insights into the emergence of star formation relations in gas-rich galaxies.

Findings

Kennicutt-Schmidt and H2-pressure relations emerge after equilibrium.

Dynamic equilibrium between ISM, stars, and feedback is crucial.

Modeling of CO formation enhances understanding of molecular gas in galaxies.

Abstract

We use time-varying models of the coupled evolution of the HI, H_2 gas phases and stars in galaxy-sized numerical simulations to: a) test for the emergence of the Kennicutt-Schmidt (K-S) and the H_2-pressure relation, b) explore a realistic H_2-regulated star formation recipe which brings forth a neglected and potentially significant SF-regulating factor, and c) go beyond typical galactic environments (for which these galactic empirical relations are deduced) to explore the early evolution of very gas-rich galaxies. In this work we model low mass galaxies ($M_{\rm baryon} \le 10^9 \msun$), while incorporating an independent treatment of CO formation and destruction, the most important tracer molecule of H2 in galaxies, along with that for the H2 gas itself. We find that both the K-S and the H_2-pressure empirical relations can robustly emerge in galaxies after a dynamic equilibrium sets in between the various ISM states, the stellar component and its feedback. (abridged)