PHANGS-JWST First Results: Destruction of the PAH Molecules in H II Regions Probed by JWST and MUSE
Sandstrom, Karin M.; Kruijssen, J. M. Diederik; Leroy, Adam K.; Rosolowsky, Erik; Chevance, Mélanie; Glover, Simon C. O.; Klessen, Ralf S.; Schinnerer, Eva; Blanc, Guillermo A.; Emsellem, Eric; Pety, Jérôme; Boquien, Médéric; Liu, Daizhong; Chastenet, Jérémy; Williams, Thomas G.; Egorov, Oleg V.; Kreckel, Kathryn; Grasha, Kathryn; Thilker, David A.; Dale, Daniel A.; Larson, Kirsten L.; Watkins, Elizabeth J.; Barnes, Ashley. T.; Bigiel, F.; Cao, Yixian; Belfiore, Francesco; Pessa, Ismael; Groves, Brent; Congiu, Enrico; Murphy, Eric J.; Pan, Hsi-An; Sutter, Jessica; Scheuermann, Fabian
Germany, United States, Australia, Finland, Italy, Chile, Belgium, France, Taiwan, Canada, United Kingdom
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.