Polycyclic Aromatic Hydrocarbons Destruction In Star-forming Regions Across 42 Nearby Galaxies

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 Z_sun), 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.

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

Comments: 19 pages, 15 figures. Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.13845 [astro-ph.GA] (or arXiv:2509.13845v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2509.13845
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Submission history
From: Oleg Egorov Dr.
[v1] Wed, 17 Sep 2025 09:20:15 UTC (7,145 KB)
https://arxiv.org/abs/2509.13845

Astrobiology, Astrochemistry,