PDRs4All VIII. Mid-infrared emission line inventory of the Orion Bar

Dries Van De Putte, Raphael Meshaka, Boris Trahin, Emilie Habart, Els Peeters, Olivier Berné, Felipe Alarcón, Amélie Canin, Ryan Chown, Ilane Schroetter, Ameek Sidhu, Christiaan Boersma, Emeric Bron, Emmanuel Dartois, Javier R. Goicoechea, Karl D. Gordon, Takashi Onaka, Alexander G.G.M. Tielens, Laurent Verstraete, Mark G. WolfireAlain Abergel, Edwin A. Bergin, Jeronimo Bernard-Salas, Jan Cami, Sara Cuadrado, Daniel Dicken, Meriem Elyajouri, Asunción Fuente, Christine Joblin, Baria Khan, Ozan Lacinbala, David Languignon, Romane Le Gal, Alexandros Maragkoudakis, Yoko Okada, Sofia Pasquini, Marc W. Pound, Massimo Robberto, Markus Röllig, Bethany Schefter, Thiébaut Schirmer, Benoit Tabone, Sílvia Vicente, Marion Zannese, Sean W.J. Colgan, Jinhua He, Gaël Rouillé, Aditya Togi, Isabel Aleman, Rebecca Auchettl, Giuseppe Antonio Baratta, Salma Bejaoui, Partha P. Bera, John H. Black, Francois Boulanger, Jordy Bouwman, Bernhard Brandl, Philippe Brechignac, Sandra Brünken, Mridusmita Buragohain, Andrew Burkhardt, Alessandra Candian, Stéphanie Cazaux, Jose Cernicharo, Marin Chabot, Shubhadip Chakraborty, Jason Champion, Ilsa R. Cooke, Audrey Coutens, Nick L.J. Cox, Karine Demyk, Jennifer Donovan Meyer, Sacha Foschino, Pedro García-Lario, Maryvonne Gerin, Carl A. Gottlieb, Pierre Guillard, Antoine Gusdorf, Patrick Hartigan, Eric Herbst, Liv Hornekaer, Lina Issa, Cornelia Jäger, Eduardo Janot-Pacheco, Olga Kannavou, Michael Kaufman, Francisca Kemper, Sarah Kendrew, Maria S. Kirsanova, Pamela Klaassen, Sun Kwok, Álvaro Labiano, Thomas S.Y. Lai, Bertrand Le Floch, Franck Le Petit, Aigen Li, Hendrik Linz, Cameron J. Mackie, Suzanne C. Madden, Joëlle Mascetti, Brett A. McGuire, Pablo Merino, Elisabetta R. Micelotta, Jon A. Morse, Giacomo Mulas, Naslim Neelamkodan, Ryou Ohsawa, Alain Omont, Roberta Paladini, Maria Elisabetta Palumbo, Amit Pathak, Yvonne J. Pendleton, Annemieke Petrignani, Thomas Pino, Elena Puga, Naseem Rangwala, Mathias Rapacioli, Jeonghee Rho, Alessandra Ricca, Julia Roman-Duval, Joseph Roser, Evelyne Roueff, Farid Salama, Dinalva A. Sales, Karin Sandstrom, Peter Sarre, Ella Sciamma-O’Brien, Kris Sellgren, Sachindev S. Shenoy, David Teyssier, Richard D. Thomas, Adolf N. Witt, Alwyn Wootten, Nathalie Ysard, Henning Zettergren, Yong Zhang, Ziwei E. Zhang, Junfeng Zhen

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

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.

Original languageEnglish
Article numberA86
JournalAstronomy and Astrophysics
Volume687
DOIs
Publication statusPublished - Jul 1 2024

Keywords

  • ISM: atoms
  • ISM: lines and bands
  • ISM: molecules
  • infrared: ISM
  • photon-dominated region (PDR)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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