Feedback in Extragalactic Star Clusters (FEAST): Spectral Energy Distributions and the Physical Properties of Star Clusters in NGC 628 with CIGALE
July 2026 • 2026ApJ..1005..227L
Abstract • With Hubble Space Telescope and James Webb Space Telescope (JWST) observations of NGC 628 spanning 0.3─7.7 μm, 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 Paα and 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission) and eYSC-II (compact Paα and diffuse 3.3 μm 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 (qPAH) 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.
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