FEAST: A NIRSpec/MOS Survey of Emerging Young Star Clusters in NGC 628
April 2026 • 2026ApJ..1001..128F
Abstract • JWST can pierce through dusty molecular clouds to study the early stages of star formation, where young star clusters are actively driving stellar feedback and still emerging from their natal cloud. We present a first look of the JWST/NIRSpec multiplex spectroscopy observations acquired by the Feedback in Emerging extrAgalactic Star clusTers program for the nearby spiral galaxy NGC 628. We showcase JWST's ability to resolve the spectral properties of emerging young star clusters (eYSCs) and their immediate interstellar medium by focusing on a bright star-forming complex (0.5 × 0.5 kpc2) in the northern spiral arm as a science proof-of-concept. The eYSC spectra are rich in ionized gas (from H II regions), as well as warm H2 and polycyclic aromatic hydrocarbon (PAH) emission from photodissociation regions (PDRs), consistent with young star formation. Paα equivalent widths and H/He ionizing photon fluxes both indicate the presence of hot, young massive stars (O8.5V─O8V), consistent with photometry spectral energy distribution estimates. The ionized gas is highly correlated with H2 and PAH emission, suggesting that the PDR morphology evolves as clusters emerge from their natal cloud. We find a photoionization-dominated regime from independent line diagnostics, with little contribution from supernovae-driven shocks, highlighting the importance of presupernovae feedback when massive stars are present. This pilot study showcases how JWST's multiplex spectroscopy mode can disentangle the mechanisms present in the youngest stages of star formation for the first time outside the Local Group.
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