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Durham University

Department of Physics

Staff profile

Publication details for Prof Carlos Frenk

Okamoto, T., Nagashima, M., Lacey, C. G. & Frenk, C. S. (2017). The metal enrichment of passive galaxies in cosmological simulations of galaxy formation. Monthly Notices of the Royal Astronomical Society 464(4): 4866-4874.

Author(s) from Durham


Massive early-type galaxies have higher metallicities and higher ratios of α elements to iron than their less massive counterparts. Reproducing these correlations has long been a problem for hierarchical galaxy formation theory, both in semi-analytic models and cosmological hydrodynamic simulations. We show that a simulation in which gas cooling in massive dark haloes is quenched by radio-mode active galactic nuclei (AGNs) feedback naturally reproduces the observed trend between α/Fe and the velocity dispersion of galaxies, σ. The quenching occurs earlier for more massive galaxies. Consequently, these galaxies complete their star formation before α/Fe is diluted by the contribution from Type Ia supernovae. For galaxies more massive than ∼1011 M⊙, whose α/Fe correlates positively with stellar mass, we find an inversely correlated mass–metallicity relation. This is a common problem in simulations in which star formation in massive galaxies is quenched either by quasar- or radio-mode AGN feedback. The early suppression of gas cooling in progenitors of massive galaxies prevents them from recapturing enriched gas ejected as winds. Simultaneously reproducing the [α/Fe]–σ relation and the mass–metallicity relation is, thus, difficult in the current framework of galaxy formation.