Clump-scale Dust Attenuation in Epoch of Reionization Galaxies: Spatially Resolved Properties from FirstLight Simulations

Abstract Understanding dust attenuation in galaxies at both integrated and spatially resolved scales is fundamental for accurately determining the physical properties of galaxies. Recent high-spatial-resolution observations with the Atacama Large Millimeter/submillimeter Array and James Webb Space Telescope enable investigations of spatially resolved properties in high-redshift galaxies ( z ≳ 6), but spatial variations in dust observables remain poorly constrained. We use cosmological zoom-in simulations combined with postprocessing dust radiative transfer calculations for 376 clumpy galaxies at z = 6–9 with stellar masses of M * ≳ 10 9 M ⊙ . For each system, we investigate dust attenuation and reemission properties for three components: system integrated, individual clumps, and diffuse regions. We find that system-integrated attenuation curves are grayer than the Calzetti curve, even when assuming Milky Way– or Small Magellanic Cloud–type dust. Attenuation curves of individual clumps are even grayer, while diffuse regions exhibit steeper curves owing to enhanced scattering in optically thin environments. Since the effects of optical depth and dust–star geometry are intrinsically degenerate in attenuation curves, we introduce a toy model based on the infrared excess (IRX)–Δ β plane, where Δ β denotes the difference between attenuated and intrinsic ultraviolet slopes. Applying this framework, we find that clumps have dust column densities approximately 1 order of magnitude higher than system-integrated values and exhibit cospatial or dust-extended geometries. In contrast, system-integrated attenuation reflects star-extended geometries driven by contributions from optically thin diffuse regions. We apply this framework to REBELS-IFU galaxies at z ∼ 7 and find good agreement with our simulation predictions.