Polycyclic Aromatic Hydrocarbon Size Tracers

We examine the dependence of polycyclic aromatic hydrocarbon (PAH) band intensity ratios as a function of the average number of carbon atoms and assess their effectiveness as tracers for PAH size, utilising the data, models, and tools provided by the NASA Ames PAH Infrared Spectroscopic Database.

To achieve this, we used spectra from mixtures of PAHs of different ionisation fractions, following a size distribution. Our work, congruent with earlier findings, shows that band ratios that include the 3.3 μm PAH band provide the best PAH size tracers for small-to-intermediate sized PAHs.

In addition, we find that band ratios that include the sum of the 15-20 μm PAH features (IΣ15−20) and the 6.2 or 7.7 μm bands also serve as good tracers for PAH size in the case of small-to-intermediate sized PAHs, for objects under a similar PAH size distribution as with the presented models. For different PAH size distributions, the application of a scaling factor to the I6.2/IΣ15−20 ratio can provide estimates for the size of the small-to-intermediate PAH population within sources.

Employment of the I6.2/IΣ15−20 and I7.7/IΣ15−20 ratios can be of particular interest for JWST observations limited only to ∼ 5-28 μm MIRI(-MRS) coverage.

A. Maragkoudakis, E. Peeters, A. Ricca, C. Boersma

Comments: 8 pages, 5 figures; Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2307.03743 [astro-ph.GA] (or arXiv:2307.03743v1 [astro-ph.GA] for this version)
Submission history
From: Alexandros Maragkoudakis
[v1] Fri, 7 Jul 2023 17:52:19 UTC (164 KB)
https://arxiv.org/abs/2307.03743
Astrobiology, Astrochemistry