PDRs4All IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar

Abstract

(Abridged) Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 $\mu$m. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR, the atomic PDR, and the HII region. We use JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extract five template spectra to represent the morphology and environment of the Orion Bar PDR. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. While the spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 $\mu$m, a wealth of weaker features and sub-components are present. We report trends in the widths and relative strengths of AIBs across the five template spectra. These trends yield valuable insight into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 $\mu$m AIB emission from class B${}_{11.2}$ in the molecular PDR to class A${}_{11.2}$ in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a "weeding out" of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called 'grandPAHs'.

25 pages, 10 figures, to appear in A&A

References in corpus (31)

• The distance to the Orion Nebula
• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point
• Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene
• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• JWST MIRI flight performance: The Medium-Resolution Spectrometer
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope III. Integral-field spectroscopy
• Laboratory formation of fullerenes from PAHs: Top-down interstellar chemistry
• Compression and ablation of the photo-irradiated cloud the Orion Bar
• The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR
• Carbon-rich dust past the asymptotic giant branch: aliphatics, aromatics, and fullerenes in the Magellanic Clouds
• The PAH emission characteristics of the reflection nebula NGC2023
• Probing the size and charge of Polycyclic Aromatic Hydrocarbons
• PDRs4All: A JWST Early Release Science Program on radiative feedback from massive stars
• Mixed aliphatic and aromatic composition of evaporating very small grains in NGC 7023 revealed by the 3.4/3.3 $\mu$m ratio
• PAH features within few hundred parsecs of active galactic nuclei
• Carriers of the mid-IR emission bands in PNe reanalysed. Evidence of a link between circumstellar and interstellar aromatic dust
• Spatial distribution and interpretation of the 3.3 \mum PAH emission band of the Red Rectangle
• Astrochemical relevance of VUV ionization of large PAH cations
• The nature of point source fringes in mid-infrared spectra acquired with the James Webb Space Telescope
• The 11.2 $\mu$m emission of PAHs in astrophysical objects
• [SiPAH]+ pi-Complexes in the Interstellar Medium
• Polycyclic Aromatic Hydrocarbon emission in Spitzer/IRS maps II: A direct link between band profiles and the radiation field strength
• DFT study on interstellar PAH molecules with aliphatic side groups
• On the Aliphatic versus Aromatic Content of the Carriers of the "Unidentified" Infrared Emission Features
• Dust evolution across the Horsehead Nebula
• Polycyclic Aromatic Hydrocarbon emission model in photodissociation regions I: Application to the 3.3, 6.2, and 11.2 $\mu$m bands
• Mechanochemical synthesis of Aromatic Infrared Band carriers. The top-down chemistry of interstellar carbonaceous dust grain analogues
• Orion Bar as a window to the evolution of PAHs
• Nano-grain depletion in photon-dominated regions
• The 3.3 $\mu$m Infrared Emission Feature: Observational and Laboratory Constraints on Its Carrier

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