Direct Abundance Maps and Radial Metallicity Gradients of Two Galaxies at z ∼ 4–5 in the GARDEN Survey

Abstract We investigate galaxies in the Galaxies at All Redshifts Deciphered and Explained with the NIRSpec microshutter array (MSA; GARDEN) survey that exhibit auroral emission lines, enabling spatially resolved measurements of electron temperature and direct oxygen abundances. Two galaxies in this survey have spectra suitable for this analysis: CANDELS 8005 at z = 3.794 and CANDELS 7986 at z = 4.702. For both galaxies, we measure auroral and key nebular emission-line fluxes across their full extent, allowing direct-method oxygen abundance determinations in individual spatial pixels (spaxels). These observations demonstrate the viability of deep JWST/NIRSpec MSA spectroscopy for spatially resolved chemical analyses at high redshift, aided by weak nebular continua and low interstellar extinction. We derive global direct abundances of log(O/H)+12 = 8.008 − 0.027 + 0.025 for CANDELS 8005 and 7.89 − 0.028 + 0.027 for CANDELS 7986. Emission-line diagnostics indicate neither galaxy hosts an active galactic nucleus. A first-order kinematic analysis suggests a potential merger in CANDELS 8005. The direct abundances are consistent with strong-line estimates based on our data and recent high-redshift calibrations. We build emission line, radial velocity, strong-line abundance indices, electron temperature, and direct abundance maps for both galaxies, thanks to the excellent spatial resolution. From the direct abundance maps, we measure linear radial metallicity gradients of − 0.11 1 − 0.025 + 0.026 dex kpc −1 for CANDELS 8005 (statistically significant) and −0.0928 ± 0.0880 dex kpc −1 for CANDELS 7986, where the large uncertainties limit the significance of the result. These results provide a rare direct measurement of a radial metallicity gradient at z > 0 from direct-method abundances, offering key observational support for inside-out galaxy growth with feedback-regulated chemical enrichment.