Polycyclic aromatic hydrocarbons destruction in star-forming regions across 42 nearby galaxies
Oleg V. Egorov, Adam K. Leroy, Karin Sandstrom, Kathryn Kreckel, Dalya Baron, Francesco Belfiore, Ryan Chown, Jessica Sutter, Médéric Boquien, Mar Canal i Saguer, Enrico Congiu, Daniel A. Dale, Evgeniya Egorova, Michael Huber, Jing Li, Thomas G. Williams, Jérémy Chastenet, I-Da Chiang, Ivan Gerasimov, Hamid Hassani, Hwihyun Kim, Hannah Koziol, Janice C. Lee, Rebecca L. McClain, José Eduardo Méndez Delgado, Hsi-An Pan, Debosmita Pathak, Erik Rosolowsky, Sumit K. Sarbadhicary, Eva Schinnerer, David Thilker, Leonardo Ubeda, Tony Weinbeck
Published: 2025/9/17
Abstract
Polycyclic aromatic hydrocarbons (PAHs) are widespread in the interstellar medium (ISM) of Solar metallicity galaxies, where they play a critical role in ISM heating, cooling, and reprocessing stellar radiation. The PAH fraction, the abundance of PAHs relative to total dust mass, is a key parameter in ISM physics. Using JWST and MUSE observations of 42 galaxies from the PHANGS survey, we analyze the PAH fraction in over 17 000 H II regions spanning a gas-phase oxygen abundance of 12+log(O/H) = 8.0-8.8 (Z ~ 0.2-1.3 Zsun), and ~400 isolated supernova remnants (SNRs). We find a significantly lower PAH fraction toward H II regions compared to a reference sample of diffuse ISM areas at matched metallicity. At 12+log(O/H) > 8.2, the PAH fraction toward H II regions is strongly anti-correlated with the local ionization parameter, suggesting that PAH destruction is correlated with ionized gas and/or hydrogen-ionizing UV radiation. At lower metallicities, the PAH fraction declines steeply in both H II regions and the diffuse ISM, likely reflecting less efficient PAH formation in metal-poor environments. Carefully isolating dust emission from the vicinity of optically-identified supernova remnants, we see evidence for selective PAH destruction from measurements of lower PAH fractions, which is, however, indistinguishable at ~50 pc scales. Overall, our results point to ionizing radiation as the dominant agent of PAH destruction within H II regions, with metallicity playing a key role in their global abundance in galaxies.