The origin of the metallicity difference between star-forming and passive galaxies: Insights from {\nu}2GC semi-analytic model

TL;DR

This study uses the nu2GC semi-analytic model to explore the metallicity difference between star-forming and passive galaxies, identifying strangulation as the main cause and emphasizing the importance of star formation timescales.

Contribution

It demonstrates that strangulation-driven quenching explains metallicity differences and highlights the diagnostic potential of metallicity in galaxy formation models.

Findings

Strangulation is the primary driver of metallicity differences.

Galaxies quenched by strangulation have higher metallicities.

Metallicity differences can diagnose star formation processes.

Abstract

We investigate the origin of the observed metallicity difference between star-forming and passive galaxies using the semi-analytic galaxy formation model nu2GC. Our fiducial model successfully reproduces the observed metallicity differences in local galaxies while simultaneously matching the potential-metallicity relations of both star-forming and passive galaxies. By varying the star formation efficiency, we identify strangulation as the primary driver of the metallicity difference. This finding highlights the critical role of star formation timescales in explaining the observed metallicity difference. Our results suggest that metallicity differences serve as a valuable diagnostic for evaluating star formation models in both semi-analytic models and cosmological simulations. Furthermore, galaxies quenched by processes resembling strangulation -- where the supply of cold gas is halted in a slowly growing halo -- exhibit higher metallicities than star-forming galaxies of the same stellar mass. In our model, this occurs in isolated, low-mass galaxies where rapid cooling leads to an effect resembling strangulation due to the discrete treatment of gas accretion onto dark matter halos. We propose that the metallicities of isolated, low-mass passive galaxies could provide key insights into refining models of hot gas halo growth.