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

TL;DR

This study uses high-resolution simulations and dust radiative transfer to analyze dust attenuation properties in early galaxies, revealing complex spatial variations and introducing a new model to interpret dust geometry effects.

Contribution

It presents the first detailed analysis of spatially resolved dust attenuation in high-redshift galaxies using cosmological simulations combined with a novel interpretive framework.

Findings

Attenuation curves are grayer than Calzetti, especially in clumps.

Clumps have higher dust column densities than system averages.

Diffuse regions show steeper attenuation curves due to scattering.

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 ALMA and JWST enable investigations of spatially resolved properties in high-redshift galaxies ($z \gtrsim 6$), but spatial variations in dust properties remain poorly constrained. We use cosmological zoom-in simulations combined with post-processing dust radiative transfer calculations for 376 clumpy galaxies at $z=6$-$9$ with stellar masses of $M_* \gtrsim 10^9 \, M_\odot$. For each system, we investigate dust attenuation and re-emission 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 MW- or SMC-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 IRX-$\Delta\beta$ plane, where $\Delta\beta$ denotes the difference between attenuated and intrinsic UV slopes. Applying this framework, we find that clumps have dust column densities approximately an order of magnitude higher than system-integrated values and exhibit co-spatial 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 $z \sim 7$ and find good agreement with our simulation predictions.