# The metallicity and elemental abundance maps of kinematically atypical galaxies for constraining minor merger and accretion histories

## TL;DR

This study uses metallicity and elemental abundance maps from integral field spectroscopy to identify signatures of minor mergers and accretion in atypical galaxies, revealing distinct kinematic and chemical features linked to their evolutionary history.

## Contribution

It demonstrates that 2D metallicity and abundance maps can effectively trace minor merger and accretion events in galaxies with unusual kinematics, which are not detectable through traditional scaling relations.

## Key findings

- KDC galaxies show flattening of [O/Fe] at large radii due to minor mergers.
- CRGD galaxies exhibit sharp metallicity transitions from center to outskirts.
- All studied galaxies are compact, indicating lack of major mergers.

## Abstract

Explaining the internal distribution and motions of stars and gas in galaxies is a key aspect in understanding their evolution. In previous work we identified five well resolved galaxies with atypical kinematics from a cosmological simulation; two had kinematically distinct cores (KDCs), and three had counter-rotating gas and stars (CRGD). In this paper, we show that i) the KDC galaxies have flattening of stellar [O/Fe] at large galacto-centric radii due to the minor mergers that gave rise to the KDCs, and ii) the CRGD galaxies have an abrupt transition in the gas metallicity maps, from high metallicity in the centre to very low metallicity further out. These galaxies are embedded in dark matter filaments where there is a ready supply of near-pristine gas to cause this effect. The non-linear increase in gas metallicity is also seen in the radial profiles, but when the metallicity gradients are measured, the difference is buried in the scatter of the relation. We also find that all five galaxies are fairly compact, with small effective radii given their stellar masses. This is because they have not experienced major mergers that kinematically heat the stars, and would have destroyed their unusual kinematics. In order to detect these signatures of minor mergers or accretion, the galaxy scaling relations or radial metallicity profiles are not enough, and it is necessary to obtain the 2D maps with integral field spectroscopy observations.