Astrochemistry

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

By Keith Cowing
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astro-ph.GA
September 22, 2025
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Polycyclic Aromatic Hydrocarbons Destruction In Star-forming Regions Across 42 Nearby Galaxies
PAH fraction anti-correlates with log([S iii]/[S ii]) (ionization parameter tracer) for thousands H ii regions in 42 PHANGS-JWST galaxies. Panel (a, b) shows all ∼ 17200 analyzed H ii regions, while ∼ 5600 brightest “resolved” H ii regions are shown on Panels (c, d). The dashed red line shows the best-fit linear regression to the “resolved” sample defined by Eq. 4. Histograms on panels (b, d) show how the logarithmic residuals after subtracting this linear trend depend on metallicity. Color on panels (a, c) denotes gas-phase oxygen abundance; red contours show the probability density of the high-metallicity (12 + log(O/H) > 8.2) points (levels correspond to 50, 65, 80, 95 and 99 percentile intervals). The Spearman correlation coefficient (ρ) and RMS scatter around the linear fit are reported on panels (a, c). — astro-ph.GA

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.

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,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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