PDRs4All
Astronomy and Astrophysics, vol. 709, pp. A39
Abstract
Context . Infrared emission from polycyclic aromatic hydrocarbons (PAHs) plays a major role in determining the charge balance of their host environments that include photodissociation regions (PDRs) in galaxies, planetary nebulae, and rims of molecular clouds. Aims . We aim to investigate the distribution and sizes of charged PAHs across the key zones of the Orion Bar PDR, i.e., the ionization front, the atomic PDR, and the dissociation fronts. Methods . We employed JWST MIRI-MRS observations of the Orion Bar from the Early Release Science program “PDRs4All” and synthetic images in the JWST MIRI filters. We investigated the spatial morphology of the aromatic infrared bands (AIBs) at 6.2, 7.7, 8.6, and 11.0 μm (commonly tracing PAH cations) and the neutral PAH-tracing 11.2 μm AIB, their (relative) correlations, and their relationship with existing empirical prescriptions for AIBs. Results . The 6.2, 7.7, 8.6, 11.0, and 11.2 μm AIBs are similar in spatial morphology on larger scales. Aside from the 11.0 μm AIB, these AIBs exhibit enhanced intensities at the dissociation fronts. Analyzing three-feature intensity correlations, two distinct groups emerge: the 8.6 and 11.0 μm AIBs versus the 6.2 and 7.7 μm AIBs. We attribute these correlations to PAH size. The 6.2 and 7.7 μm AIBs trace cationic, medium-sized PAHs. Quantum chemical calculations reveal that the 8.6 μm AIB is carried by large, compact, cationic PAHs, and the 11.0 μm AIB's correlation with it implies that this band is as well. The 6.2/8.6 and 7.7/8.6 PAH band ratios thus probe PAH size. We conclude that the 6.2/11.2 AIB ratio is the most reliable proxy for charged PAHs within the cohort. We outline JWST MIRI imaging prescriptions that serve as effective tracers of the PAH ionization fraction, as traced by the 7.7/11.2 PAH emission. Conclusions . This study showcases the efficacy of the 6−9 μm AIBs in probing the charge state and size distribution of emitting PAHs, offering insights into the physical conditions of their host environments. JWST MIRI photometry offers a viable alternative to IFU spectroscopy for characterizing this emission in extended objects.
Authors 26
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Affiliation as printed
Department of Physics & Astronomy, The University of Western Ontario
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Western University · Search for Extraterrestrial Intelligence
Affiliation as printed
Carl Sagan Center, SETI Institute
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
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Leiden University · Leiden Observatory · University of Maryland, College Park
Affiliation as printed
Astronomy Department, University of Maryland
Leiden Observatory, Leiden University
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Affiliation as printed
Department of Astronomy, Graduate School of Science, The University of Tokyo
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Western University · Search for Extraterrestrial Intelligence
Affiliation as printed
Carl Sagan Center, SETI Institute
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
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Affiliation as printed
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
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Affiliation as printed
NASA Ames Research Center
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Affiliation as printed
Dipartimento di Fisica, Università degli Studi di Milano
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Université Toulouse III - Paul Sabatier · Institut de Recherche en Astrophysique et Planétologie
Affiliation as printed
Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier
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Université Toulouse III - Paul Sabatier · Institut de Recherche en Astrophysique et Planétologie
Affiliation as printed
Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier
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Western University · The Ohio State University
Affiliation as printed
Astronomy Department, Ohio State University
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
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Université Paris-Saclay · Institut des Sciences Moléculaires d'Orsay
Affiliation as printed
Institut des Sciences Moléculaires d'Orsay, Université Paris-Saclay
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Consejo Superior de Investigaciones Científicas · Instituto de Física Fundamental
Affiliation as printed
Instituto de Física Fundamental (CSIC)
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Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Institut d'Astrophysique Spatiale, Université Paris-Saclay
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Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Institut d'Astrophysique Spatiale, Université Paris-Saclay
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Affiliation as printed
NASA Ames Research Center
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Affiliation as printed
Department of Physics, Institute of Science, Banaras Hindu University (BHU)
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Ames Research Center · Search for Extraterrestrial Intelligence
Affiliation as printed
Carl Sagan Center, SETI Institute
NASA Ames Research Center
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Affiliation as printed
Astrophysical Institute and University Observatory
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Universidade Federal do Rio Grande
Affiliation as printed
Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande
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Université Toulouse III - Paul Sabatier · Institut de Recherche en Astrophysique et Planétologie
Affiliation as printed
Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier
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Affiliation as printed
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
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Space Telescope Science Institute · Université Paris-Saclay · Institut d'Astrophysique Spatiale
Affiliation as printed
Institut d'Astrophysique Spatiale, Université Paris-Saclay
Space Telescope Science Institute
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Western University · Space Telescope Science Institute
Affiliation as printed
Department of Physics & Astronomy, The University of Western Ontario
Institute for Earth and Space Exploration, The University of Western Ontario
Space Telescope Science Institute
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Affiliation as printed
School of Physics and Astronomy, Sun Yat-sen University
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Affiliation as printed
Atomic Physics Division, Stockholm University
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