Effective yields as tracers of feedback effects on metallicity scaling relations in the EAGLE cosmological simulations

Abstract

Effective yields, 𝑦eff, are defined by fundamental galaxy properties (i.e., stellar mass -𝑀★-, gas mass -𝑀gas- and gas-phase metallicity). For a closed-box model, 𝑦eff is constant and equivalent to the mass in metals returned to the gas per unit mass locked in long-lived stars. Deviations from such behaviour have been often considered observational signatures of past feedback events. By analysing EAGLE simulations with different feedback models, we evaluate the impact of supernovae (SN) and active galactic nuclei (AGN) feedback on 𝑦eff at redshift 𝑧 = 0. When removing supermassive black holes (BH) and, hence, AGN effects, in simulations, galaxies are located around a plane in the 𝑀★ − 𝑀gas − O/H parameter space (being O/H a proxy for gas metallicity, as usual), with such a plane roughly describing a surface of constant 𝑦eff. As the ratio between BH mass and 𝑀★ increases, galaxies deviate from that plane towards lower 𝑦eff as a consequence of AGN feedback. For galaxies not strongly affected by AGN feedback, a stronger SN feedback efficiency generates deviations towards lower 𝑦eff, while galaxies move towards the opposite side of the plane (i.e., towards higher values of 𝑦eff) as SN feedback becomes weaker. Star-forming galaxies observed in the Local Universe are located around a similar 3D plane. Our results suggest that the features of the scatter around the observed plane are related to the different feedback histories of galaxies, which might be traced by 𝑦eff.