Unveiling Metal Mixing in a Grand-design Spiral: A UV/Optical Multiphase Spatially Resolved Study of M83

Abstract We present a spatially resolved, multiphase study of chemical enrichment around young star clusters (YSCs) in the nearby grand-design spiral M83 by combining far-ultraviolet (UV) absorption-line spectroscopy from the Hubble Space Telescope Cosmic Origins Spectrograph with cospatial optical spectroscopy from the Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) and the Large Binocular Telescope (LBT) Multi-Object Double Spectrograph (MODS). Our sample includes 18 YSCs spanning spectroscopic ages of ∼1–6 Myr and galactocentric radii out to R / R 25 = 0.56. Neutral (H i ) abundances were derived from UV absorption-line spectroscopy and compared with ionized (H ii ) abundances from reddening-corrected optical emission lines. Because auroral lines are not detected in all regions, we develop and apply an empirical multizone electron-temperature ( T e ) calibration based on strong-line diagnostics to estimate T e and derive reliable nebular abundances. We measure oxygen (O), sulphur (S), nitrogen (N), and iron (Fe) abundances, tracing enrichment from distinct nucleosynthetic channels. The α -elements (O and S) exhibit similar behaviour, consistent with enrichment by core-collapse supernovae, whereas Fe shows weaker variations, reflecting its delayed production by Type Ia supernovae. Nitrogen displays the largest phase offset (ionized–neutral), with enhancements of up to ΔN/H ∼ 1.5 dex and ΔN/O > 1.5 dex in the ionized gas relative to the neutral phase, indicating localized enrichment by massive stars and inefficient mixing between gas phases on Myr timescales. While the ionized gas exhibits signatures of feedback-regulated chemical enrichment and large-scale abundance gradients, corresponding trends are weak or absent in the neutral gas, consistent with metals remaining largely confined to the immediate star-forming environment during the earliest stages of cluster evolution in a massive grand-design spiral.