Modeling the interstellar aromatic infrared bands with co-added spectra of PAHs

TL;DR

This study models interstellar aromatic infrared bands by co-adding spectra of PAHs of different sizes, revealing how PAH populations influence observed spectral features in various astrophysical environments.

Contribution

It introduces a new modeling approach using co-added spectra of PAHs across size groups to interpret variations in interstellar infrared bands.

Findings

Good profile match with observations for the 7.7 μm complex.

Medium-sized PAH cations dominate the 7.6 μm sub-feature.

Large PAH cations are associated with the 7.8 μm component.

Abstract

The observed variations in profiles of the interstellar aromatic infrared bands correlate with the object type and are indicative of PAH populations existing i n different sources. Spectroscopic studies on PAHs can provide tools for the int erpretation of variations accompanying the AIBs. As the observed spectra results from a mix of possible species in the region attempt is made to model this comp osite spectra by co-adding emissions from PAHs in different size groups. Theoretical IR data of PAHs having 10 to 96 carbon atoms is used to obtain emis sion spectra. The models are taken in size groups making up of small, medium and large PAHs. The models show good profile match with observations for the 7.7 $\mu m$ complex having sub-features at 7.6 and 7.8 $\mu m$. The 7.6 $\mu m$ sub-feature dominates in the spectra of medium sized PAH cations matching observations from UV rich interstellar environments. The 7.8 $\mu m$ component is more intense in the spectra of large PAH cations (model III) correlating with observations from benign astrophysical regions. A possible interpretation for the observations of $C-H$ out-of-plane bend modes and the weak outliers on the blue side of the intense 11.2 $\mu m$ band is proposed. The models provide pointers to possible PAH populations in different regions.