Mass-Metallicity Relation during the Epoch of Reionization in the CROC Simulations

TL;DR

This study uses CROC simulations to analyze the mass-metallicity relation during the Epoch of Reionization (redshifts 5-10), revealing similarities across redshifts and insights into galaxy metallicity evolution, with implications for future JWST observations.

Contribution

The paper provides the first detailed analysis of the high-redshift mass-metallicity relation in the CROC simulations, highlighting its characteristics and limitations.

Findings

MZR flattens with higher stellar mass across all redshifts.

Gas and stellar metallicities are similar but diverge with galaxy age.

CROC's star formation suppression affects metallicity predictions.

Abstract

The low-redshift mass-metallicity relation (MZR) is well studied, but the high-redshift MZR remains difficult to observe. To study the early MZR further, we analyze the Cosmic Reionization on Computers (CROC) simulations with a focus on the MZR from redshifts 5 to 10. We find that, across all redshifts, CROC galaxies exhibit similar stellar-phase and gas-phase MZRs that flatten with higher stellar mass. We attribute this flattening to the inaccurate star formation and feedback modeling in CROC (star formation is overly suppressed in massive CROC galaxies). In addition, we show that the ratio between stellar metallicity and gas metallicity ($Z_*/Z_{gas}$) decreases as stellar age increases, meaning that in CROC galaxies, gas accretion rate is lower than metal production rate. With JWST we will be able to compare our predictions to observations of the Epoch of Reionization and understand better early galaxy formation.