Scaling relations of metallicity, stellar mass, and star formation rate in metal-poor starbursts: II. Theoretical models

TL;DR

This paper develops multi-phase chemical evolution models to explain the observed scaling relations of metallicity, stellar mass, and star formation rate in galaxies across redshifts up to 3, highlighting different star formation modes.

Contribution

It introduces a theoretical framework that reproduces observed galaxy scaling relations and explains deviations through distinct star formation modes.

Findings

Models successfully reproduce observed scaling relations up to z~3.

Deviations are explained by active and passive star formation modes.

Predicts molecular cloud fraction as a function of stellar mass.

Abstract

Scaling relations of metallicity (O/H), star formation rate (SFR), and stellar mass give important insight on galaxy evolution. They are obeyed by most galaxies in the Local Universe and also at high redshift. In a companion paper, we compiled a sample of ~1100 galaxies from redshift 0 to ~3, spanning almost two orders of magnitude in metal abundance, a factor of $\sim10^6$ in SFR, and of ~10^5 in stellar mass. We have characterized empirically the star-formation "main sequence" (SFMS) and the mass-metallicity relation (MZR) for this sample, and also identified a class of low-metallicity starbursts, rare locally but more common in the distant universe. These galaxies deviate significantly from the main scaling relations, with high SFR and low metal content for a given M*. In this paper, we model the scaling relations and explain these deviations from them with a set of multi-phase chemical evolution models based on the idea that, independently of redshift, initial physical conditions in a galaxy's evolutionary history can dictate its location in the scaling relations. Our models are able to successfully reproduce the O/H, M*, and SFR scaling relations up to z~3, and also successfully predict the molecular cloud fraction as a function of stellar mass. These results suggest that the scaling relations are defined by different modes of star formation: an "active" starburst mode, more common at high redshift, and a quiescent "passive" mode that is predominant locally and governs the main trends.