2025ApJ...995...43A

We present an analysis of rest-frame UV continuum slopes, β, using a sample of 1011 galaxies at 6.5 < z < 13 from the EPOCHS photometric sample collated from the GTO PEARLS and public ERS/GTO/GO (JADES, CEERS, NGDEEP, GLASS) JWST/NIRCam imaging across $178.9\,{{\rm{arcmin}}}^{2}$ of unmasked blank sky. We correct our UV slopes for the photometric error coupling bias using 200,000 power-law spectral energy distributions for each β = {-1, -1.5, -2, -2.5, -3} in each field, finding biases as large as Δβ ≃ -0.55 for the lowest signal-to-noise ratio galaxies in our sample. Additionally, we simulate the impact of rest-UV line emission (including Lyα) and damped Lyα systems on our measured β, finding biases as large as 0.5-0.6 for the most extreme systems. We find a decreasing trend with redshift of β = -1.51 ± 0.08 - (0.097 ± 0.010) × z, with potential evidence for Population III stars or top-heavy initial mass functions in a subsample of 68 β + σ_β < -2.8 galaxies. At z ≃ 11.5, we measure an extremely blue β(M_UV = -19) = -2.73 ± 0.06, deviating from simulations, indicative of low-metallicity galaxies with nonzero Lyman continuum escape fractions f_esc,LyC ≳ 0 and minimal dust content. The observed steepening of $d\beta /d{{\rm{log}}}_{10}({M}_{\star }/{M}_{\odot })$ from 0.22 ± 0.02 at z ≃ 7 to 0.81 ± 0.13 at z ≃ 11.5 implies that dust produced in core-collapse supernovae at early times may be ejected via outflows from low-mass galaxies. We also observe a flatter dβ/dM_UV = 0.03 ± 0.02 at z ≃ 7 and a shallower $d\beta /d\,{{\rm{log}}}_{10}({M}_{\star }/{M}_{\odot })$ at z < 11 than seen by the Hubble Space Telescope, unveiling a new population of low-mass, faint galaxies reddened by dust produced in the stellar winds of asymptotic giant branch stars or carbon-rich Wolf-Rayet binaries.