Feedback in Emerging extragAlactic Star clusTers, FEAST: JWST spots PAH destruction in NGC 628 during the emerging phase of star formation (2406.01666v2)

Abstract: We investigate the emergence phase of young star clusters in the nearby spiral galaxy NGC 628. We use JWST NIRCam and MIRI observations to create spatially resolved maps of the Pa$\alpha$-1.87 $\mu$m and Br$\alpha$-4.05 $\mu$m hydrogen recombination lines, as well as the 3.3 $\mu$m and 7.7 $\mu$m emission from polycyclic aromatic hydrocarbons (PAHs). We extract 953 compact HII regions and analyze the PAH emission and morphology at $\sim$10 pc scales in the associated photo-dissociation regions (PDRs). While HII regions remain compact, radial profiles help us to define three PAH morphological classes: compact ($\sim$ 42%), extended ($\sim$ 34%) and open ($\sim$ 24%). The majority of compact and extended PAH morphologies are associated with very young star clusters ($<$5 Myr), while open PAH morphologies are mainly associated with star clusters older than 3 Myr. We observe a general decrease in the 3.3 $\mu$m and 7.7 $\mu$m PAH band emission as a function of cluster age, while their ratio remains constant with age out to 10 Myr and morphological class. The recovered PAH${3.3 \mu{\rm m}}$/PAH${7.7 \mu{\rm m}}$ ratio is lower than values reported in the literature for reference models that consider neutral and ionized PAH populations and analyses conducted at galactic scales. The 3.3 $\mu$m and 7.7 $\mu$m bands are typically associated to neutral and ionised PAHs, respectively. While we expected neutral PAHs to be suppressed in proximity of the ionizing source, the constant PAH${3.3 \mu{\rm m}}$/PAH${7.7 \mu{\rm m}}$ ratio would indicate that both families of molecules disrupt at similar rates in proximity of the HII regions.