Carbonaceous em. band sub-comp. in NGC7023

Nearly all emission maps peak at the dissociation front (DF1), while the relative intensity in the atomic hydrogen region (ATM) varies strongly. We classify the features into spatial distribution types based on the intensity ratio in ATM relative to DF1. Most bands are of type I (low ATM/DF1; 3.3, 3.4, 5.2, 5.7, 11.3um) or II (medium ATM/DF1; 16.2, 7.7, 8.6, 12.7, 16.4um), while only few are of type III (high ATM/DF1; 11.0, 17.4um).

A breakdown of the 5.7, 7.7, 11.3 and 12.7um bands into blue and red sub-components reveals that contributions on the blue side are of type III, while those on the red side are of type I or II. These strongly differing spatial distributions reveal that at least two different populations contribute to the 16-18um range, and that these populations are also connected to the profiles of the 5.7, 7.7, 11.3, and 12.7um bands.

The maps further indicate a continued evolution of these profiles toward the central cavity of NGC7023, where fullerene emission (C60) was previously detected. We speculate that the population of emission carriers could be in an intermediate photochemical evolution stage that precedes fullerene formation.