Feedback in Extragalactic Star Clusters (FEAST): Spectral Energy Distributions and the Physical Properties of Star Clusters in NGC 628 with CIGALE

With Hubble Space Telescope and James Webb Space Telescope (JWST) observations of NGC 628 spanning 0.3–7.7 μ m, we fit the spectral energy distributions of over 12,000 optically selected star clusters, emerging young star clusters (eYSCs), and MIRI-selected sources with CIGALE to derive their ages, masses, extinctions, and dust properties. We find that near-IR selected eYSC-I (compact Pa α and 3.3 μ m polycyclic aromatic hydrocarbon (PAH) emission) and eYSC-II (compact Pa α and diffuse 3.3 μ m PAH emission) sources peak at ∼3–5 Myr, where ∼12% of the clusters have an E ( B − V ) > 2, demonstrating the presence of dust-embedded populations as clusters emerge. Further, the distributions of the fractional PAH abundance ( q PAH ) and stellar-to-nebular attenuation ratio ( E ( B − V ) ⋆ / E ( B − V ) neb ) suggest an evolutionary sequence in which sources evolve from eYSC-I to eYSC-II as clusters clear their surrounding dust and gas. The photodissociation region clearing timescale inferred from the ratio of eYSC-I to optically visible stellar clusters is ∼4 Myr. Additionally, we find that star clusters in the spiral arms of NGC 628 are preferentially more massive and more dust reddened than those in interarm regions. Finally, we find that ∼65% of eYSC-I, ∼27% of eYSC-II, and ∼40% of F335M-selected sources coincide with an F770W peak in our MIRI-selected catalog within 4 pixels, confirming that F770W-bright sources preferentially trace the youngest and dustiest regions. Overall, our results highlight the ability of JWST together with CIGALE model grids to identify and characterize eYSCs during their short-lived embedded phases, and provide constraints on the feedback mechanisms that govern the emergence of stellar clusters.