2025MNRAS.539..109F

We present measurements of the dust attenuation curves of 12 massive ($9~<~\log$($M_{\star }$/${\rm M}_{\odot }$) $<~10$) Lyman-break galaxies at $z=6.5 \!\!-\!\! 7.7$ derived from JWST NIRSpec integral field unit spectroscopy. The galaxies are drawn from the Atacama Large Millimeter/submillimeter Array Reionization Era Bright Emission Line Survey (REBELS) large program. The dust attenuation curves were obtained by fitting spectral energy distribution (SED) models with a flexible dust attenuation curve to the full galaxy spectra over observed wavelengths $0.6 \!\!-\!\! 5.3\ \mu$m. These attenuation curves show a range of recovered slopes ($-0.41\le \delta \le 0.09$) that are on average slightly flatter than seen in local sources of the same stellar masses, with none exhibiting very steep slopes. Three galaxies exhibit evidence for a 2175 Å dust bump ($> \!\! 4\sigma$) and we find that SED fitting excluding the bump can overestimate derived stellar masses by up to 0.4 dex. Correcting for the dust attenuation with our best-fitting attenuation curves, we recover a range of intrinsic ultraviolet slopes ($-2.4<\beta _0{<}-2.0$). The galaxies show moderate reddening ($A_{V,\text{ stellar}}~\begin{tex}\simeq\end{tex}0.1 \!\!-\!\! 0.6$ mag) and the $A_{V,\text{ stellar}}$ to stellar mass relation is consistent with local sources. The attenuation curve slope is found to correlate with $A_{V,\text{ stellar}}$, while we see no strong correlation with stellar mass, ${M_{\rm UV}}$, or gas-phase metallicity. Overall, our results show little evolution in dust properties in the REBELS sources compared to the local Universe. Comparing our recovered trends to empirical models suggests that the most important factor driving the variation in the attenuation curves in our sample is the dust-star geometry, not the properties of the dust grains themselves.