Polycyclic aromatic hydrocarbon destruction in star-forming regions across 42 nearby galaxies

¹ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg, Germany
² Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210, USA
³ Center for Cosmology and Astroparticle Physics, 191 West Woodruff Avenue, Columbus, OH 43210, USA
⁴ Department of Astronomy & Astrophysics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
⁵ Kavli Institute for Particle Astrophysics & Cosmology, Stanford University, CA, 94305, USA
⁶ Center for Decoding the Universe, Stanford University, CA, 94305, USA
⁷ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50157 Firenze, Italy
⁸ Whitman College, 345 Boyer Avenue, Walla Walla, WA 99362, USA
⁹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06000 Nice, France
¹⁰ Dr. Karl-Remeis Sternwarte and Erlangen Centre for Astroparticle Physics, Friedrich-Alexander Universitat Erlangen-Nurnberg, Sternwartstr. 7, 96049 Bamberg, Germany
¹¹ European Southern Observatory (ESO), Alonso de Córdova 3107, Casilla 19, Santiago 19001, Chile
¹² Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA
¹³ Sub-department of Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹⁴ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, B-9000 Gent, Belgium
¹⁵ Institute of Astronomy and Astrophysics, Academia Sinica, No. 1, Sec. 4, Roosevelt Road, Taipei 106319, Taiwan
¹⁶ Department of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada
¹⁷ International Gemini Observatory, NSF NOIRLab, 950 N Cherry Ave, Tucson, AZ 85719, USA
¹⁸ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁹ Instituto de Astronomía, Universidad Nacional Autónoma de México, Ap. 70-264, 04510 CDMX, Mexico
²⁰ Department of Physics,Tamkang University, No.151, Yingzhuan Rd., Tamsui Dist., New Taipei City 251301, Taiwan
²¹ Max-Planck-Institutfür Astronomie, Künigstuhl 17, D-69117 Heidelberg, Germany
²² Department of Physics and Astronomy,The Johns Hopkins University, Baltimore, MD 21218, USA

^⋆ Corresponding author: oleg.egorov@uni-heidelberg.de

Received: 15 July 2025
Accepted: 17 September 2025

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are widespread in the interstellar medium (ISM) of near 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 analyzed 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_⊙), 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 H II regions and in 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 of 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; metallicity plays a key role in their global abundance in galaxies.