Spatially Resolved Gas-phase Metallicity in FIRE-2 Dwarfs: Late-Time Evolution of Metallicity Relations in Simulations with Feedback and Mergers

TL;DR

This study uses FIRE-2 simulations to analyze the spatially resolved gas-phase metallicity in dwarf galaxies, finding close agreement with observations and insights into metallicity uniformity and effects of mergers.

Contribution

It provides the first detailed comparison of spatially resolved metallicity relations in simulated dwarf galaxies with observational data, including effects of feedback and mergers.

Findings

Simulated dwarf galaxies match observed mass-metallicity relations.

Metallicity is nearly uniform across different ISM phases within 0.1 dex.

Major mergers significantly impact metallicity distribution and trigger starbursts.

Abstract

We present an analysis of spatially resolved gas-phase metallicity relations in five dwarf galaxies ($M_{halo} \approx 10^{11} M_\odot$, $M_\star \approx 10^{8.8}-10^{9.6} M_\odot$) from the FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulation suite, which include an explicit model for sub-grid turbulent mixing of metals in gas, near $z\approx 0$, over a period of 1.4 Gyrs, and compare our findings with observations. While these dwarf galaxies represent a diverse sample, we find that all simulated galaxies match the observed mass-metallicity (MZR) and mass-metallicity gradient (MZGR) relations. We note that in all five galaxies, the metallicities are effectively identical between phases of the interstellar medium (ISM), with 95$\%$ being within $\pm$0.1 dex between various ISM phases, including the cold and dense gas ($T < 500$ K and $n_{\rm H} > 1$ cm$^{-3}$), ionized gas (near the H$\alpha$ $T \approx 10^4$ K ridge-line), and nebular regions (ionized gas where the 10 Myr-averaged star formation rate is non-zero). We find that most of the scatter in relative metallicity between cold and dense gas and ionized gas/nebular regions can be attributed to either local starburst events or metal-poor inflows. We also note the presence of a major merger in one of our galaxies, m11e, with a substantial impact on the metallicity distribution in the spatially resolved map, showing two strong metallicity peaks and triggering a starburst in the main galaxy.