The Stellar Populations and Rest-frame Colors of Star-forming Galaxies at z  ≈ 8: Exploring the Impact of Filter Choice and Star Formation History Assumption with JADES

Our understanding of the physical properties of star-forming galaxies during the Epoch of Reionization (EoR; at z > 6) suffers from degeneracies among the apparent properties of the stars, nebular gas, and dust. These degeneracies are most prominent with photometry, which has insufficient (1) spectral resolution and (2) rest-frame spectral coverage. We explore ways to break these degeneracies with a sample of N = 22 high-redshift star-forming galaxies at 7 < z phot ≤ 9, using some of the deepest existing imaging from JWST/NIRCam and JWST/MIRI with JADES. Key to this study is the imaging from JWST/MIRI at 7.7 μ m, which provides coverage of the rest-frame I band at the observed redshifts. We infer stellar population properties and rest-frame colors using a variety of filter sets and star formation history (SFH) assumptions to explore the impact of these choices. Evaluating these quantities both with and without the 7.7 μ m data point shows that dense spectral coverage with JWST/NIRCam (eight or more filters, including at least one medium-band at λ obs ≈ 4–5 μ m) can compensate for lacking the rest-frame I -band coverage for the vast majority (≈80%) of our sample. Furthermore, these galaxy properties are most consistently determined by assuming the delayed-tau SFH, which provides the smallest offsets and scatters around these offsets when including JWST/MIRI. Within extragalactic surveys like JADES and CEERS, our findings suggest that robust characterization of the stellar population properties and rest-frame colors for typical high-redshift star-forming galaxies (i.e., galaxies with M UV ≈ −20 and β UV ≈ −2) is possible with JWST/NIRCam alone at z ≈ 8.