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Arxiv: PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar Published: 10/13/2023 12:07:14 AM Updated: 10/13/2023 12:07:14 AM

Paper abstract: (Abridged) We investigate the impact of radiative feedback from massive starson their natal cloud and focus on the transition from the HII region to theatomic PDR (crossing the ionisation front (IF)), and the subsequent transitionto the molecular PDR (crossing the dissociation front (DF)). We usehigh-resolution near-IR integral field spectroscopic data from NIRSpec on JWSTto observe the Orion Bar PDR as part of the PDRs4All JWST Early Release ScienceProgram. The NIRSpec data reveal a forest of lines including, but not limitedto, HeI, HI, and CI recombination lines, ionic lines, OI and NI fluorescencelines, Aromatic Infrared Bands (AIBs including aromatic CH, aliphatic CH, andtheir CD counterparts), CO2 ice, pure rotational and ro-vibrational lines fromH2, and ro-vibrational lines HD, CO, and CH+, most of them detected for thefirst time towards a PDR. Their spatial distribution resolves the H and Heionisation structure in the Huygens region, gives insight into the geometry ofthe Bar, and confirms the large-scale stratification of PDRs. We observenumerous smaller scale structures whose typical size decreases with distancefrom Ori C and IR lines from CI, if solely arising from radiative recombinationand cascade, reveal very high gas temperatures consistent with the hotirradiated surface of small-scale dense clumps deep inside the PDR. The H2lines reveal multiple, prominent filaments which exhibit differentcharacteristics. This leaves the impression of a "terraced" transition from thepredominantly atomic surface region to the CO-rich molecular zone deeper in.This study showcases the discovery space created by JWST to further ourunderstanding of the impact radiation from young stars has on their natalmolecular cloud and proto-planetary disk, which touches on star- and planetformation as well as galaxy evolution.