The Metallicity and Elemental Abundance Gradients of Simulated Galaxies, and their Environmental Dependence

TL;DR

This study uses cosmological simulations to analyze how galaxy mergers and feedback processes influence metallicity and elemental abundance gradients, revealing their evolutionary paths and environmental dependence.

Contribution

It provides new insights into the formation and evolution of metallicity gradients in galaxies, especially considering AGN feedback and galaxy mergers, aligning with observational data.

Findings

Massive galaxies have flatter metallicity gradients due to mergers.

Gradients evolve through initial steepness, passive evolution, and flattening by mergers.

Weak environmental dependence observed in gradient variations.

Abstract

The internal distribution of heavy elements, in particular the radial metallicity gradient, offers insight into the merging history of galaxies. Using our cosmological, chemodynamical simulations that include both detailed chemical enrichment and feedback from active galactic nuclei (AGN), we find that stellar metallicity gradients in the most massive galaxies ($\sim3\times10^{10}$M$_\odot$) are made flatter by mergers and are unable to regenerate due to the quenching of star formation by AGN feedback. The fitting range is chosen on a galaxy-by-galaxy basis in order to mask satellite galaxies. The evolutionary paths of the gradients can be summarised as follows; i) creation of initial steep gradients by gas-rich assembly, ii) passive evolution by star formation and/or stellar accretion at outskirts, iii) sudden flattening by mergers. There is a significant scatter in gradients at a given mass, which originates from the last path, and therefore from galaxy type. Some variation remains at given galaxy mass and type because of the complexity of merging events, and hence we find only a weak environmental dependence. Our early-type galaxies (ETGs), defined from the star formation main sequence rather than their morphology, are in excellent agreement with the observed stellar metallicity gradients of ETGs in the SAURON and ATLAS3D surveys. We find small positive [O/Fe] gradients of stars in our simulated galaxies, although they are smaller with AGN feedback. Gas-phase metallicity and [O/Fe] gradients also show variation, the origin of which is not as clear as for stellar populations.