PDRs4All

III. JWST’s NIR spectroscopic view of the Orion Bar^★

¹ Department of Physics & Astronomy, The University of Western Ontario, London ON N6A 3K7, Canada
² Institute for Earth and Space Exploration, The University of Western Ontario, London ON N6A 3K7, Canada
³ Carl Sagan Center, SETI Institute, 339 Bernardo Avenue, Suite 200, Mountain View, CA 94043, USA
⁴ Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, Bâtiment 121, 91405 Orsay Cedex, France
⁵ Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier, CNRS, CNES, 9 Av. du colonel Roche, 31028 Toulouse Cedex 04, France
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁷ Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA
⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Astronomy Department, University of Maryland, College Park, MD 20742, USA
¹⁰ Institut des Sciences Moléculaires d’Orsay, Université Paris-Saclay, CNRS, Bâtiment 520, 91405 Orsay Cedex, France
¹¹ Instituto de Física Fundamental (CSIC), Calle Serrano 121-123, 28006, Madrid, Spain
¹² NASA Ames Research Center, MS 245-6, Moffett Field, CA 940351000, USA
¹³ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Bunkyo-ku, Tokyo 113-0033, Japan
¹⁴ Department of Physics, Faculty of Science and Engineering, Meisei University, 2-1-1 Hodokubo, Hino, Tokyo 191-8506, Japan
¹⁵ Instituto de Astrofísica e Ciências do Espaço, Tapada da Ajuda, Edifício Leste, 2 ° Piso, 1349-018 Lisboa, Portugal
¹⁶ ACRI-ST, Centre d’Etudes et de Recherche de Grasse (CERGA), 10 Av. Nicolas Copernic, 06130 Grasse, France
¹⁷ INCLASS Common Laboratory, 10 Av. Nicolas Copernic, 06130 Grasse, France
¹⁸ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 92190 Meudon, France
¹⁹ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill EH9 3HJ, UK
²⁰ Observatorio Astronómico Nacional (OAN,IGN), Alfonso XII, 3, 28014 Madrid, Spain
²¹ Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium
²² Quantum Solid State Physics (QSP), Celestijnenlaan 200d – Box 2414, 3001 Leuven, Belgium
²³ Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes, CNRS, 38000 Grenoble, France
²⁴ Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, 38406 Saint-Martin d’Hères, France
²⁵ I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
²⁶ Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA
²⁷ Physikalischer Verein – Gesellschaft für Bildung und Wissenschaft, Robert-Mayer-Str. 2, 60325 Frankfurt, Germany
²⁸ Goethe-Universität, Physikalisches Institut, Frankfurt am Main, Germany
²⁹ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
³⁰ Instituto de Física e Química, Universidade Federal de Itajubá, Av. BPS 1303, Pinheirinho, 37500-903, Itajubá, MG, Brazil
³¹ Institute of Mathematics and Statistics, University of São Paulo, Rua do Matão, 1010, Cidade Universitária, Butantã, 05508-090 São Paulo, SP, Brazil
³² Instituto de Física e Química, Universidade Federal de Itajubá, Av. BPS 1303, Pinheirinho, 37500-903 Itajubá, MG, Brazil
³³ Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA
³⁴ Australian Synchrotron, Australian Nuclear Science and Technology Organisation (ANSTO), Victoria, Australia
³⁵ INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
³⁶ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
³⁷ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
³⁸ Department of Chemistry, University of Colorado, Boulder, CO 80309, USA
³⁹ Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, CO 80303, USA
⁴⁰ Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
⁴¹ Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
⁴² School of Physics, University of Hyderabad, Hyderabad, Telangana 500046, India
⁴³ Department of Physics, Wellesley College, 106 Central Street, Wellesley, MA 02481, USA
⁴⁴ Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands
⁴⁵ Delft University of Technology, Delft, The Netherlands
⁴⁶ Laboratoire de Physique des deux infinis Irène Joliot-Curie, Université Paris-Saclay, CNRS/IN2P3, B â timent 104, 91405 Orsay Cedex, France
⁴⁷ Department of Chemistry, GITAM school of Science, GITAM Deemed to be University, Bangalore, India
⁴⁸ Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
⁴⁹ Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada
⁵⁰ National Radio Astronomy Observatory (NRAO), 520 Edgemont Road, Charlottesville, VA 22903, USA
⁵¹ European Space Astronomy Centre (ESAC/ESA), Villanueva de la Cañada, 28692 Madrid, Spain
⁵² Observatoire de Paris, PSL University, Sorbonne Université, LERMA, CNRS, 75014, Paris, France
⁵³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵⁴ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁵⁵ Institut Universitaire de France, Ministère de l’Enseignement Supérieur et de la Recherche, 1 rue Descartes, 75231 Paris Cedex 05, France
⁵⁶ Department of Physics and Astronomy, Rice University, Houston, TX 77005-1892, USA
⁵⁷ Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming, 650216, PR China
⁵⁸ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, PR China
⁵⁹ Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁶⁰ InterCat and Dept. Physics and Astron., Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁶¹ Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, 07743 Jena, Germany
⁶² Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05509-090 São Paulo, SP, Brazil
⁶³ Department of Physics and Astronomy, San José State University, San Jose, CA 95192, USA
⁶⁴ European Space Agency, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶⁵ Institute of Astronomy, Russian Academy of Sciences, 119017, Pyatnitskaya str., 48 , Moscow, Russia
⁶⁶ Department of Earth, Ocean, & Atmospheric Sciences, University of British Columbia, British Columbia V6T 1Z4, Canada
⁶⁷ Telespazio UK for ESA, ESAC, 28692 Villanueva de la Cañada, Madrid, Spain
⁶⁸ IPAC, California Institute of Technology, Pasadena, CA, USA
⁶⁹ LAB, Université de Bordeaux, CNRS, B18N, 33615 Pessac, France
⁷⁰ Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
⁷¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷² Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
⁷³ Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California – Berkeley, Berkeley, CA, USA
⁷⁴ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁷⁵ Institut des Sciences Moléculaires, CNRS, Université de Bordeaux, 33405 Talence, France
⁷⁶ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷⁷ Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Ines de la Cruz 3, 28049 Madrid, Spain
⁷⁸ Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
⁷⁹ Steward Observatory, University of Arizona, Tucson, AZ 85721-0065, USA
⁸⁰ AstronetX PBC, 55 Post Rd W FL 2, Westport, CT 06880, USA
⁸¹ Department of Physics, College of Science, United Arab Emirates University (UAEU), Al-Ain 15551, UAE
⁸² National Astronomical Observatory of Japan, National Institutes of Natural Science, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸³ Department of Physics, Institute of Science, Banaras Hindu University, Varanasi 221005, India
⁸⁴ University of Central Florida, Orlando, FL 32765, USA
⁸⁵ Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD Amsterdam, The Netherlands
⁸⁶ Laboratoire de Chimie et Physique Quantiques LCPQ/IRSAMC, UMR5626, Université de Toulouse (UPS) and CNRS, Toulouse, France
⁸⁷ Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande, 96201-900 Rio Grande, RS, Brazil
⁸⁸ Center for Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
⁸⁹ School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
⁹⁰ Astronomy Department, Ohio State University, Columbus, OH 43210, USA
⁹¹ Space Science Institute, 4765 Walnut St., R203, Boulder, CO 80301, USA
⁹² Department of Physics, Stockholm University, 10691 Stockholm, Sweden
⁹³ Department of Physics, Texas State University, San Marcos, TX 78666, USA
⁹⁴ Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606, USA
⁹⁵ School of Physics and Astronomy, Sun Yat-sen University, 2 Da Xue Road, Tangjia, Zhuhai 519000, Guangdong Province, PR China
⁹⁶ Star and Planet Formation Laboratory, 0-0 S(RIKEN Cluster for Pioneering Research, Hirosawa 2-1, Wako, Saitama 351-0198, Japan
⁹⁷ Institute of Deep Space Sciences, Deep Space Exploration Laboratory, Hefei 230026, PR China
⁹⁸ Departamento de Astronomía, Universidad de Chile, Las Condes, 7591245 Santiago, Chile
⁹⁹ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy

Received: 12 October 2023
Accepted: 22 December 2023

Abstract

Context. JWST has taken the sharpest and most sensitive infrared (IR) spectral imaging observations ever of the Orion Bar photodis-sociation region (PDR), which is part of the nearest massive star-forming region the Orion Nebula, and often considered to be the ‘prototypical’ strongly illuminated PDR.

Aims. We investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the H II region to the atomic PDR – crossing the ionisation front (IF) –, and the subsequent transition to the molecular PDR – crossing the dissociation front (DF). Given the prevalence of PDRs in the interstellar medium and their dominant contribution to IR radiation, understanding the response of the PDR gas to far-ultraviolet (FUV) photons and the associated physical and chemical processes is fundamental to our understanding of star and planet formation and for the interpretation of any unresolved PDR as seen by JWST.

Methods. We used high-resolution near-IR integral field spectroscopic data from NIRSpec on JWST to observe the Orion Bar PDR as part of the PDRs4All JWST Early Release Science programme. We constructed a 3″ × 25″’ spatio-spectral mosaic covering 0.97– 5.27 μm at a spectral resolution R of ~2700 and an angular resolution of 0.075″–0.173″. To study the properties of key regions captured in this mosaic, we extracted five template spectra in apertures centred on the three H₂ dissociation fronts, the atomic PDR, and the H II region. This wealth of detailed spatial-spectral information was analysed in terms of variations in the physical conditions-incident UV field, density, and temperature – of the PDR gas.

Results. The NIRSpec data reveal a forest of lines including, but not limited to, He I, H I , and C I recombination lines; ionic lines (e.g. Fe III and Fe II); O I and N I fluorescence lines; aromatic infrared bands (AIBs, including aromatic CH, aliphatic CH, and their CD counterparts); pure rotational and ro-vibrational lines from H₂; and ro-vibrational lines from HD, CO, and CH⁺, with most of them having been detected for the first time towards a PDR. Their spatial distribution resolves the H and He ionisation structure in the Huygens region, gives insight into the geometry of the Bar, and confirms the large-scale stratification of PDRs. In addition, we observed numerous smaller-scale structures whose typical size decreases with distance from θ¹ Ori C and IR lines from C I , if solely arising from radiative recombination and cascade, reveal very high gas temperatures (a few 1000 K) consistent with the hot irradiated surface of small-scale dense clumps inside the PDR. The morphology of the Bar, in particular that of the H₂ lines, reveals multiple prominent filaments that exhibit different characteristics. This leaves the impression of a ‘terraced’ transition from the predominantly atomic surface region to the CO-rich molecular zone deeper in. We attribute the different characteristics of the H₂ filaments to their varying depth into the PDR and, in some cases, not reaching the C⁺/C/CO transition. These observations thus reveal what local conditions are required to drive the physical and chemical processes needed to explain the different characteristics of the DFs and the photochemical evolution of the AIB carriers.

Conclusions. This study showcases the discovery space created by JWST to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star and planet formation as well as galaxy evolution.