PHANGS–JWST First Results: Destruction of the PAH Molecules in H ii Regions Probed by JWST and MUSE

Journal article

Abstract Polycyclic aromatic hydrocarbons (PAHs) play a critical role in the reprocessing of stellar radiation and balancing the heating and cooling processes in the interstellar medium but appear to be destroyed in H ii regions. However, the mechanisms driving their destruction are still not completely understood. Using PHANGS–JWST and PHANGS–MUSE observations, we investigate how the PAH fraction changes in about 1500 H ii regions across four nearby star-forming galaxies (NGC 628, NGC 1365, NGC 7496, and IC 5332). We find a strong anticorrelation between the PAH fraction and the ionization parameter (the ratio between the ionizing photon flux and the hydrogen density) of H ii regions. This relation becomes steeper for more luminous H ii regions. The metallicity of H ii regions has only a minor impact on these results in our galaxy sample. We find that the PAH fraction decreases with the Hα equivalent width—a proxy for the age of the H ii regions—although this trend is much weaker than the one identified using the ionization parameter. Our results are consistent with a scenario where hydrogen-ionizing UV radiation is the dominant source of PAH destruction in star-forming regions.

Authors: Egorov, OV; Kreckel, K; Sandstrom, KM; Leroy, AK; Glover, SCO

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal Letters
• Volume: 944
• Issue: 2
• Pages: L16-L16
• Publication date: 2023-02-16
• DOI: 10.3847/2041-8213/acac92
• EISSN: 2041-8213
• ISSN: 2041-8205
• Language: English
• Keywords: Ion; Star formation; Astrophysics; Hydrogen; Physics; Metallicity; Galaxy; Ionization