The evolution of the mass-metallicity relation in galaxies of different morphological types

TL;DR

This study uses chemical evolution models to explore how the mass-metallicity relation varies with galaxy morphology and redshift, suggesting different galaxy types dominate at different cosmic times.

Contribution

It introduces a method to incorporate galaxy formation epochs and refine mass grids, providing insights into the evolution of the mass-metallicity relation across galaxy types.

Findings

The mass-metallicity relation is mainly driven by star formation efficiency, not outflows.

High-redshift galaxies (z=3.5) are likely proto-ellipticals.

At z=2.2, a mix of proto-spirals and proto-ellipticals is observed.

Abstract

By means of chemical evolution models for ellipticals, spirals and irregular galaxies, we aim at investigating the physical meaning and the redshift evolution of the mass-metallicity relation as well as how this relation is connected with galaxy morphology. {abridged} We assume that galaxy morphologies do not change with cosmic time. We present a method to account for a spread in the epochs of galaxy formation and to refine the galactic mass grid. (abridged) We compare our predictions to observational results obtained for galaxies between redshifts 0.07 and 3.5. We reproduce the mass-metallicity (MZ) relation mainly by means of an increasing efficiency of star formation with mass in galaxies of all morphological types, without any need to invokegalactic outflows favoring the loss of metals in the less massive galaxies. Our predictions can help constraining the slope and the zero point of the observed local MZ relation, both affected by uncertainties related to the use of different metallicity calibrations. We show how, by considering the MZ, the O/H vs star formation rate (SFR), and the SFR vs galactic mass diagrams at various redshifts, it is possible to constrain the morphology of the galaxies producing these relations. Our results indicate that the galaxies observed at z=3.5 should be mainly proto-ellipticals, whereas at z=2.2 the observed galaxies consist of a morphological mix of proto-spirals and proto-ellipticals. At lower redshifts, the observed MZ relation is well reproduced by considering both spirals and irregulars. (abridged)