A Study of Polycyclic Aromatic Hydrocarbon Emission in 30 Dor as seen by JWST

TL;DR

This study uses JWST observations to analyze PAH emission in the low-metallicity environment of 30 Dor, revealing differences in PAH properties compared to higher-metallicity regions and suggesting inhibited growth of larger PAHs.

Contribution

It provides a detailed comparison of PAH emission characteristics in 30 Dor and the Orion Bar, highlighting environmental effects on PAH size distribution and ionization.

Findings

PAH emission profiles are similar in 30 Dor and Orion Bar

PAHs in 30 Dor have higher ionization and smaller sizes

Lower metallicity inhibits growth of larger PAHs

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are responsible for strong mid-IR emission features near star-forming regions. It is well known that low-metallicity environments exhibit weaker PAH emission, but it is not clear how the metallicity affects the properties of the emitting PAH population. We present a detailed study of the PAH emission in the low-metallicity regime represented by 30 Dor in the Large Magellanic Cloud (LMC) and we compare it to the PAH emission in the Orion Bar to investigate the characteristics of the PAH population and how the environments affects the resulting IR emission. We analyze JWST observations of 30 Dor that include imaging (NIRCam, MIRI) and spectroscopy (NIRSpec/IFU, MIRI/MRS). We extracted NIRSpec/IFU and MIRI/MRS spectra from 18 apertures that cover the morphological structures of 30 Dor. We characterize the profiles and relative intensities of PAH emission in these apertures. The detailed profiles of the PAH emission bands in 30 Dor are all very similar, and compare well to those from one of the dissociation fronts (DF2) in the Orion Bar. The relative band ratios on the other hand show a much larger range than in the Orion Bar. The PAH emission in 30 Dor originates from a population with a higher ionization fraction than in the Orion Bar, and a size distribution that has more smaller PAHs. Since smaller PAHs typically photo-fragment before larger PAHs, our findings support the hypothesis that the lower PAH emission for lower metallicities is the result of inhibition of growth toward larger PAHs rather than photo-fragmentation.