2025MNRAS.539.2685L

We present a spatially resolved analysis of four star-forming galaxies at $z = 4.44-5.64$ using data from the JWST Public Release Imaging for Extragalactic Research (PRIMER) and ALMA-[C II] Resolved ISm in STar-forming galaxies with ALma (CRISTAL) surveys to probe the stellar and interstellar medium properties on the sub-${\rm kpc}$ scale. In the $1-5\, \mu {\rm m}$ JWST NIRCam imaging we find that the galaxies are composed of multiple clumps (between 2 and ∼8) separated by $\simeq 5\, {\rm kpc}$, with comparable morphologies and sizes in the rest-frame ultraviolet (UV) and optical. Using BAGPIPES to perform pixel-by-pixel spectral energy distribution (SED) fitting to the JWST data, we show that the star formation rate (SFR) ($\simeq 25\, {\rm M}_{\odot }\,{\rm yr^{ -1}}$) and stellar mass (${\rm log}_{10}(M_{\star }/{\rm M}_{\odot })$ $\simeq 9.5$) derived from the resolved analysis are in close ($\lesssim 0.3\, {\rm dex}$) agreement with those obtained by fitting the integrated photometry. In contrast to studies of lower mass sources, we thus find a reduced impact of outshining of the older (more massive) stellar populations in these normal $z \simeq 5$ galaxies. Our JWST analysis recovers bluer rest-frame UV slopes ($\beta \simeq -2.1$) and younger ages ($\simeq 100\, {\rm Myr}$) than archival values. We find that the dust continuum from ALMA-CRISTAL seen in two of these galaxies correlates, as expected, with regions of redder rest-frame UV slopes and the SED-derived ${A_{\rm V}}$, as well as the peak in the stellar mass map. We compute the resolved ${\rm IRX}$-$\beta$relation, showing that the IRX is consistent with the local starburst attenuation curve and further demonstrating the presence of an inhomogeneous dust distribution within the galaxies. A comparison of the CRISTAL sources to those from the FirstLight zoom-in simulation of galaxies with the same $M_{\star }$ and SFR reveals similar age and colour gradients, suggesting that major mergers may be important in the formation of clumpy galaxies at this epoch.