Mapping Multi-Phase Metals in Star-forming Galaxies: a spatially resolved UV + Optical Study of NGC 5253

TL;DR

This study provides a detailed spatially-resolved comparison of chemical abundances in different gas phases within the star-forming galaxy NGC 5253, revealing differential enrichment processes and phase-dependent abundance evolution.

Contribution

It introduces a novel multi-phase, spatially-resolved analysis combining UV and optical spectroscopy to study chemical abundances in a dwarf galaxy.

Findings

Neutral gas abundances are lower than ionized gas by 0.22-0.80 dex.

N, O, and N/O abundances decrease with age in ionized gas but increase in neutral gas.

Chemical enrichment occurs first in ionized gas and later mixes into neutral gas over 10-15 Myr.

Abstract

We present a pioneering spatially-resolved, multi-phase gas abundance study on the blue compact dwarf galaxy NGC~5253, targeting 10 star-forming (SF) clusters inside six FUV HST/COS pointings with co-spatial optical VLT/MUSE observations throughout the galaxy. The SF regions span a wide range of ages (1--15 Myr) and are distributed at different radii (50 -- 230 pc). We performed robust absorption-line profile fitting on the COS spectra, covering 1065--1430 \AA\ in the FUV, allowing an accurate computation of neutral-gas abundances for 13 different ions sampling 8 elements. These values were then compared with the ionized-gas abundances, measured using the direct method on MUSE integrated spectra inside analog COS apertures. Our multi-phase, spatially resolved comparisons find abundances which are lower in the neutral gas than the ionized gas by 0.22 dex, 0.80 dex and 0.58 dex for log(O/H), log(N/H) and log(N/O), respectively. We modeled the chemical abundance distributions and evaluated correlations as a function of radius and age. It was found that while N, O and N/O abundances decrease as a function of age in the ionized gas, they increase with age in the neutral gas. No strong correlations for N, O or N/O were observed as a function of radius. The N/O and N/H offsets between the phases were found to decrease with age, providing evidence that chemical enrichment happens differentially, first in the ionized-gas phase around 2--5 Myrs (due to N-rich Wolf-Rayet stars) and then mixing out into the cold neutral gas on longer timescales of 10--15 Myr.