Diversity and evolution of dust-attenuation curves from redshift z ~ 1 to 9

The UV–optical dust-attenuation curve is key to interpreting the intrinsic properties of galaxies and provides insights into the nature of dust grains and their geometry relative to stars. We constrained the UV-optical slope of the stellar attenuation curve using a spectroscopic-redshift sample of ∼ 3,800 galaxies at z∼ 1-9 to characterize the diversity and redshift evolution of stellar attenuation curves and to gain insight into dust production and evolution at high redshifts. The sample was constructed from three JWST/NIRCam grism surveys in GOODS-S, GOODS-N, and Abell-2744 fields, with a wealth of JWST/NIRCam and HST photometry. With constraints from spectroscopic redshifts and emission line fluxes, we use the Bayesian inference framework of SED fitting code with a flexible dust model to derive the attenuation curve for each galaxy. We find that the attenuation curve slope varies strongly with Prospector at all redshifts, becoming flatter at higher attenuation, attributed to the effect of scattering, dust-star geometry, and ISM chemical evolution. We find no strong correlation between attenuation curve slope and size or axis ratio, and the trends with stellar mass and star-formation rate are largely driven by their correlation with . We find strong evidence that at fixed , the curve becomes flatter with increasing redshift. On average, the attenuation curves derived here are shallower than those at z∼ 0 and than the SMC curve. The highest redshift galaxies at z = 7-9 (124 galaxies -- a significantly larger sample than in previous studies) show slopes even flatter than the Calzetti curve, implying reduced UV obscuration and lower IR luminosities than expected from an SMC dust curve, by as large as an order of magnitude. Hydrodynamical simulations that couple dust growth to gas chemical enrichment successfully reproduce the different loci of high- and low-redshift galaxies in the slope– diagram, suggesting that dust in high-redshift galaxies is increasingly dominated by large grains produced in supernova ejecta with limited ISM processing at early times.