Exploring Chemical Homogeneity in Dwarf Galaxies: A VLT-MUSE study of JKB 18

TL;DR

This study uses VLT/MUSE integral field spectroscopy to analyze the chemical homogeneity of the dwarf galaxy JKB 18, revealing significant inhomogeneities in metallicity that challenge previous assumptions about such galaxies.

Contribution

It provides the first detailed spatially-resolved chemical abundance map of JKB 18, demonstrating inhomogeneity and exploring its origins through simulations, thus advancing understanding of dwarf galaxy evolution.

Findings

JKB 18 exhibits large-scale chemical inhomogeneity (~0.5-0.6 dex dispersions).

Standard explanations like gas accretion or Wolf-Rayet star enrichment do not account for inhomogeneity.

Supernova-driven gas removal and star-formation timing may cause observed chemical variations.

Abstract

Deciphering the distribution of metals throughout galaxies is fundamental in our understanding of galaxy evolution. Nearby, low-metallicity, star-forming dwarf galaxies in particular can offer detailed insight into the metal-dependent processes that may have occurred within galaxies in the early Universe. Here we present VLT/MUSE observations of one such system, JKB 18, a blue diffuse dwarf galaxy with a metallicity of only 12+log(O/H)=7.6$\pm$0.2 (~0.08 Zsol). Using high spatial-resolution integral field spectroscopy of the entire system, we calculate chemical abundances for individual HII regions using the direct method and derive oxygen abundance maps using strong-line metallicity diagnostics. With large-scale dispersions in O/H, N/H and N/O of ~0.5-0.6 dex and regions harbouring chemical abundances outside this 1$\sigma$ distribution, we deem JKB 18 to be chemically inhomogeneous. We explore this finding in the context of other chemically inhomogeneous dwarf galaxies and conclude that neither the accretion of metal-poor gas, short mixing timescales, or self-enrichment from Wolf-Rayet stars are accountable. Using a galaxy-scale, multi-phase, hydrodynamical simulation of a low-mass dwarf galaxy, we find that chemical inhomogeneities of this level may be attributable to the removal of gas via supernovae and the specific timing of the observations with respect to star-formation activity. This study not only draws attention to the fact that dwarf galaxies can be chemically inhomogeneous, but also that the methods used in the assessment of this characteristic can be subject to bias.