PDRs4All

VIII. Mid-infrared emission line inventory of the Orion Bar

¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
e-mail: dvandeputte@stsci.edu
² Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, Bâtiment 121, 91405 Orsay Cedex, France
³ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 92190 Meudon, France
⁴ Department of Physics & Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
⁵ Institute for Earth and Space Exploration, The University of Western Ontario, London ON N6A 3K7, Canada
⁶ Carl Sagan Center, SETI Institute, 339 Bernardo Avenue, Suite 200, Mountain View, CA 94043, USA
⁷ Institut de Recherche en Astrophysique et Planétologie, Université Toulouse III – Paul Sabatier, CNRS, CNES, 9 Av. du colonel Roche, 31028 Toulouse Cedex 04, France
⁸ Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA
⁹ Astronomy Department, Ohio State University, Columbus, OH 43210, USA
¹⁰ NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000, USA
¹¹ Institut des Sciences Moléculaires d’Orsay, Université Paris-Saclay, CNRS, Bâtiment 520, 91405 Orsay Cedex, France
¹² Instituto de Física Fundamental (CSIC), Calle Serrano 121-123, 28006 Madrid, Spain
¹³ Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium
¹⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Bunkyo-ku, Tokyo 113-0033, Japan
¹⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁶ Astronomy Department, University of Maryland, College Park, MD 20742, USA
¹⁷ ACRI-ST, Centre d’Etudes et de Recherche de Grasse (CERGA), 10 Av. Nicolas Copernic, 06130 Grasse, France
¹⁸ INCLASS Common Laboratory, 10 Av. Nicolas Copernic, 06130 Grasse, France
¹⁹ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill EH9 3HJ, UK
²⁰ Centro de Astrobiología (CSIC-INTA),Ctra de Torrejón a Ajaalvir, km 4, 28850 Torrejón de Ardoz, Spain
²¹ Quantum Solid State Physics (QSP), Celestijnenlaan 200d, Box 2414, 3001 Leuven, Belgium
²² Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Université Grenoble Alpes, CNRS, 38000 Grenoble, France
²³ Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, 38406 Saint-Martin-d’Hères, France
²⁴ I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
²⁵ Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
²⁶ Physikalischer Verein – Gesellschaft für Bildung und Wissenschaft, Robert-Mayer-Str. 2, 60325 Frankfurt, Germany
²⁷ Goethe-Universität, Physikalisches Institut, Frankfurt am Main, Germany
²⁸ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁹ Instituto de Astrofísica e Ciências do Espaço, Tapada da Ajuda, Edifício Leste, 2 o Piso, 1349-018 Lisboa, Portugal
³⁰ Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, PR China
³¹ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, PR China
³² Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³³ 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
³⁴ Department of Physics, Texas State University, San Marcos, TX 78666, USA
³⁵ Instituto de Física e Química, Universidade Federal de Itajubá, Av. BPS 1303, Pinheirinho, 37500-903, Itajubá, MG, Brazil
³⁶ Institute of Mathematics and Statistics, University of São Paulo, Rua do Matão, 1010, Cidade Universitária, Butantã, 05508-090, São Paulo, SP, Brazil
³⁷ Australian Synchrotron, Australian Nuclear Science and Technology Organisation (ANSTO), Victoria, Australia
³⁸ INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
³⁹ Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA
⁴⁰ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
⁴¹ Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
⁴² Department of Chemistry, University of Colorado, Boulder, CO 80309, USA
⁴³ Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, CO 80303, USA
⁴⁴ Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
⁴⁵ Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
⁴⁶ School of Physics, University of Hyderabad, Hyderabad, Telangana 500046, India
⁴⁷ Department of Physics, Wellesley College, 106 Central Street, Wellesley, MA 02481, USA
⁴⁸ Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands
⁴⁹ Delft University of Technology, Delft, The Netherlands
⁵⁰ Laboratoire de Physique des deux infinis Irène Joliot-Curie, Université Paris-Saclay, CNRS/IN2P3, Bâtiment 104, 91405 Orsay Cedex, France
⁵¹ Department of Chemistry, GITAM school of Science, GITAM Deemed to be University, Bangalore, India
⁵² Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
⁵³ Department of Chemistry, The University of British Columbia, Vancouver, British Columbia, Canada
⁵⁴ National Radio Astronomy Observatory (NRAO), 520 Edgemont Road, Charlottesville, VA 22903, USA
⁵⁵ European Space Astronomy Centre (ESAC/ESA), Villanueva de la Cañada, 28692 Madrid, Spain
⁵⁶ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France
⁵⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵⁸ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98bis bd Arago, 75014 Paris, France
⁵⁹ Institut Universitaire de France, Ministère de l’Enseignement Supérieur et de la Recherche, 1 rue Descartes, 75231 Paris Cedex 05, France
⁶⁰ Department of Physics and Astronomy, Rice University, Houston, TX 77005-1892, USA
⁶¹ Departments of Chemistry and Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁶² InterCat and Department Physics and Astron., Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
⁶³ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05509-090 Sao Paulo, SP, Brazil
⁶⁴ Department of Physics and Astronomy, San José State University, San Jose, CA 95192, USA
⁶⁵ Institut de Ciencies de l’Espai (ICE, CSIC), Can Magrans, s/n, 08193 Bellaterra, Barcelona, Spain
⁶⁶ ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
⁶⁷ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁶⁸ European Space Agency, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
⁶⁹ Institute of Astronomy, Russian Academy of Sciences, 119017, Pyatnitskaya str. 48, Moscow, Russia
⁷⁰ Department of Earth, Ocean, & Atmospheric Sciences, University of British Columbia V6T 1Z4, Canada
⁷¹ Telespazio UK for ESA, ESAC, 28692 Villanueva de la Cañada, Madrid, Spain
⁷² IPAC, California Institute of Technology, Pasadena, CA, USA
⁷³ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁷⁴ Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
⁷⁵ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷⁶ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
⁷⁷ Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California – Berkeley, Berkeley, California, USA
⁷⁸ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
⁷⁹ Institut des Sciences Moléculaires, CNRS, Université de Bordeaux, 33405 Talence, France
⁸⁰ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁸¹ Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Ines de la Cruz 3, 28049 Madrid, Spain
⁸² Department of Physics, PO Box 64, 00014 University of Helsinki, Finland
⁸³ AstronetX PBC, 55 Post Rd W FL 2, Westport, CT 06880, USA
⁸⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
⁸⁵ Department of Physics, College of Science, United Arab Emirates University (UAEU), Al-Ain, 15551, UAE
⁸⁶ National Astronomical Observatory of Japan, National Institutes of Natural Science, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸⁷ Department of Physics, Institute of Science, Banaras Hindu University, Varanasi 221005, India
⁸⁸ University of Central Florida, Orlando, FL 32765, USA
⁸⁹ Van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁹⁰ Laboratoire de Chimie et Physique Quantiques LCPQ/IRSAMC, UMR5626, Université de Toulouse (UPS) and CNRS, Toulouse, France
⁹¹ Department of Physics and Astronomy, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul, 08826, South Korea
⁹² Instituto de Matemática, Estatística e Física, Universidade Federal do Rio Grande, 96201-900 Rio Grande, RS, Brazil
⁹³ Center for Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
⁹⁴ School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
⁹⁵ Space Science Institute, 4765 Walnut St., R203, Boulder, CO 80301, USA
⁹⁶ Department of Physics, Stockholm University, 10691 Stockholm, Sweden
⁹⁷ Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606, USA
⁹⁸ School of Physics and Astronomy, Sun Yat-sen University, 2 Da Xue Road, Tangjia, Zhuhai 519000, Guangdong Province, PR China
⁹⁹ Star and Planet Formation Laboratory, 0–0 S, RIKEN Cluster for Pioneering Research, Hirosawa 2–1, Wako, Saitama 351-0198, Japan
¹⁰⁰ Institute of Deep Space Sciences, Deep Space Exploration Laboratory, Hefei 230026, PR China

Received: 19 January 2024
Accepted: 20 April 2024

Abstract

Context. Mid-infrared emission features are important probes of the properties of ionized gas and hot or warm molecular gas, which are difficult to probe at other wavelengths. The Orion Bar photodissociation region (PDR) is a bright, nearby, and frequently studied target containing large amounts of gas under these conditions. Under the “PDRs4All” Early Release Science Program for JWST, a part of the Orion Bar was observed with MIRI integral field unit (IFU) spectroscopy, and these high-sensitivity IR spectroscopic images of very high angular resolution (0.2″) provide a rich observational inventory of the mid-infrared (MIR) emission lines, while resolving the H II region, the ionization front, and multiple dissociation fronts.

Aims. We list, identify, and measure the most prominent gas emission lines in the Orion Bar using the new MIRI IFU data. An initial analysis summarizes the physical conditions of the gas and demonstrates the potential of these new data and future IFU observations with JWST.

Methods. The MIRI IFU mosaic spatially resolves the substructure of the PDR, its footprint cutting perpendicularly across the ionization front and three dissociation fronts. We performed an up-to-date data reduction, and extracted five spectra that represent the ionized, atomic, and molecular gas layers. We identified the observed lines through a comparison with theoretical line lists derived from atomic data and simulated PDR models. The identified species and transitions are summarized in the main table of this work, with measurements of the line intensities and central wavelengths.

Results. We identified around 100 lines and report an additional 18 lines that remain unidentified. The majority consists of H I recombination lines arising from the ionized gas layer bordering the PDR. The H I line ratios are well matched by emissivity coefficients from H recombination theory, but deviate by up to 10% because of contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni. We show how the Ne III/Ne II, S IV/S III, and Ar III/Ar II ratios trace the conditions in the ionized layer bordering the PDR, while Fe III/Fe II and Ni III/Ni II exhibit a different behavior, as there are significant contributions to Fe II and Ni II from the neutral PDR gas. We observe the pure-rotational H₂ lines in the vibrational ground state from 0–0 S(1) to 0–0 S (8), and in the first vibrationally excited state from 1–1 S (5) to 1–1 S(9). We derive H₂ excitation diagrams, and for the three observed dissociation fronts, the rotational excitation can be approximated with one thermal (~700 K) component representative of an average gas temperature, and one nonthermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model of the Orion Bar PDR, and find that the predicted excitation matches the data qualitatively, while adjustments to the parameters of the PDR model are required to reproduce the intensity of the 0–0 S (6) to S (8) lines.