Weak Evolution of the Mass-metallicity Relation at Cosmic Dawn in the FirstLight Simulations

Abstract

Little is known about the mass-metallicity relation in galaxies at cosmic dawn, z=5-15. This paper uses the FirstLight database of cosmological simulations to predict the mass-metallicity relation at z=5-8. There is weak evolution of the metallicity with redshift at a fixed stellar mass. This is mostly driven by the weak evolution of the gas fraction at these high redshifts. Emission lines ratios, such as [OIII]lambda5007/Hbeta, are relatively good tracers of metallicity and stellar mass with an abrupt decrease of the line luminosities at low metallicities and low masses driven by the low metal abundances at these early times.