paper

JWST Observations of Photo-dissociation Regions. II. Aliphatic/Aromatic Carbonaceous Dust, Ices, and Gas Phase Spectral Line Inventory

arXiv:2506.20468 · doi:10.1051/0004-6361/202554851

Abstract

This paper provides an overview of the spectroscopic data obtained by the JWST Guaranteed Time Observations (GTO) program 1192, "The Physics and Chemistry of PDR Fronts", including an inventory of the spatially resolved dust, gas, and molecular content in the Horsehead nebula and the NW filament of NGC~7023. We demonstrate the unique capability of this high spatial resolution data set to elucidate the evolution of gas and dust at the interface between stars and their natal clouds at the scale at which the physics and chemistry occur. The Disassociation Regions (PDRs) in the Horsehead nebula and the North West (NW) filament of NGC 7023 were mapped with a spectral resolution 1000-3000 and a spatial resolution of ~2e-4 pc between 0.97-28um. Spectra extracted from template regions yield a large number of atomic, ionized, and molecular lines. Full line lists and extracted spectra for all 10 regions are provided through CDS. Absorption from HO, CO, and CO ices are identified in 3 regions in NGC 7023. In this overview, we have focused on the spectral region between 3 and 5 um which is dominated by emission from aromatic and aliphatic carbon bonds to illustrate the power of the data set. We confirm the entrainment of aromatic carbonaceous species in the photo-evaporative flow from the PDR surface into the H\,{\sc{ii}} region in the Horsehead. No aliphatic emission is present in the outflow, indicating the complete removal of aliphatic bonds when exposed to strong UV fields. There is a clear detection of deuterium substitution in the carbon bonds. Aliphatic D-substitution is more efficient relative to aromatic D-substitution, ranging from N/N ~ 0.1-0.3 for aliphatics compared to ~0.03 for the aromatics.

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