Polycyclic Aromatic Hydrocarbon Emission In Galaxies As Seen With JWST

By Keith Cowing
Status Report
June 18, 2024
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Polycyclic Aromatic Hydrocarbon Emission In Galaxies As Seen With JWST
JWST MIRI/MRS spatially maps of the [NeIII]/[NeII] emission lines. From top left (clockwise): NGC 7469, NGC 3256-N, NGC 3256-S, VV114, IIZw96 and NGC 5728.The apertures shown in Figure 2 are shown here as well. — astro-ph.GA

We present a systematic study of mid-infrared spectra of galaxies including star-forming galaxies and Active Galactic Nuclei observed with JWST MIRI-MRS and NIRSpec-IFU.

We focus on the relative variations of the 3.3, 6.2, 7.7, 11.3, 12.7 and 17 micron Polycyclic Aromatic Hydrocarbon (PAH) features within spatially resolved regions of galaxies including NGC 3256, NGC 7469, VV 114, II Zw96 and NGC 5728. Using theoretical PAH models and extending our earlier work, we introduce a new PAH diagnostic involving the 17 micron PAH feature. To determine the drivers of PAH band variations in galaxies, we compare observed PAH spectral bands to predictions from theoretical PAH models.

We consider extinction, dehydrogenation and PAH size and charge as possible drivers of PAH band variations. We find a surprising uniformity in PAH size distribution among the spatially resolved regions of the galaxies studied here, with no evidence for preferential destruction of the smallest grains, contrary to earlier findings. Neither extinction nor dehydrogenation play a crucial role in setting the observed PAH bands.

Instead, we find that PAH charge plays a significant role in PAH inter-band variations. We find a tight relation between PAH charge and the intensity of the radiation field as traced by the [NeIII]/[NeII] maps.

In agreement with recent JWST results, we find a predominance of neutral PAH molecules in the nuclei of Active Galaxies and their outflows. Ionised PAHs are the dominant population in star-forming galaxies. We discuss the implications of our findings for the use of PAHs as ISM tracers in high redshift galaxies.

Dimitra Rigopoulou, Fergus R. Donnan, Ismael García-Bernete, Miguel Pereira-Santaella, Almudena Alonso-Herrero, Ric Davies, Leslie K. Hunt, Patrick F. Roche, Taro Shimizu

Comments: 16 pages, 13 figures, accepted for publication by MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2406.11415 [astro-ph.GA] (or arXiv:2406.11415v1 [astro-ph.GA] for this version)
Submission history
From: Dimitra Rigopoulou
[v1] Mon, 17 Jun 2024 11:04:02 UTC (2,263 KB)

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) 🖖🏻