The ALPINE-CRISTAL-JWST Survey: NIRSpec IFU Data Processing and Spatially-resolved Views of Chemical Enrichment in Normal Galaxies at z=4-6

Abstract

We present a statistical study of spatially resolved chemical enrichment in 18 main-sequence galaxies at $z=4$--6, observed with \jwst/NIRSpec IFU as part of the ALPINE-CRISTAL-\jwst\ survey. Performing an optimized reduction and calibration procedure, including local background subtraction, light-leakage masking, stripe removal, and astrometry refinement, we achieve robust emission-line mapping on kiloparsec scales. Although line-ratio distributions vary across galaxies in our sample, we generally find mild central enhancements in [O\,\textsc{iii}]/H${\hat{I}}^2$, [O\,\textsc{ii}]/[O\,\textsc{iii}], [S\,\textsc{ii}]${}_{6732}$/[S\,\textsc{ii}]${}_{6718}$, H$\hat{I}\pm$/H${\hat{I}}^2$, and $L_{\mathrm{H}\hat{\mathrm{I}}\pm }/L_{\mathrm{UV}}$, consistent with elevated electron density, dust obscuration, and bursty star formation accompanied by reduced metallicity and ionization parameter. These features point to inside-out growth fueled by recent inflows of pristine gas. Nevertheless, the median metallicity gradient is nearly flat over a few kpc scale, $\hat{I}”\log (O/H)=0.02\pm 0.01$ dex kpc${}^{-1}$, implying efficient chemical mixing through inflows, outflows, and mergers. From pixel-by-pixel stellar and emission-line characterizations, we further investigate the resolved Fundamental Metallicity Relation (rFMR). Metallicity is described by a fundamental plane with stellar mass and SFR surface densities, but with a stronger dependence on $\hat{I}{\pounds }_{\mathrm{SFR}}$ than seen in local galaxies. Our results indicate that the regulatory processes linking star formation, gas flows, and metal enrichment were already vigorous $\sim$1 Gyr after the Big Bang, producing the nearly flat metallicity gradient and a stronger coupling between star formation and metallicity than observed in evolved systems in the local universe.

37 pages, 15 figures, 2 tables. Comments are welcome. Please also see coordinated papers on today's arxiv (Faisst et al; Tsujita et al.)