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Journal Articles Astron.Astrophys. Year : 2024

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

Ryan Chown , Ameek Sidhu , Els Peeters , Alexander G.G.M Tielens , Jan Cami , Olivier Berné (1) , Emilie Habart (2) , Felipe Alarcón , Amélie Canin (1) , Ilane Schroetter (1) , Boris Trahin (2) , Dries van de Putte , Alain Abergel (2) , Edwin A Bergin , Jeronimo Bernard-Salas (3) , Christiaan Boersma , Emeric Bron (4) , Sara Cuadrado , Emmanuel Dartois (5) , Daniel Dicken , Meriem El-Yajouri (2) , Asunción Fuente , Javier R Goicoechea , Karl D Gordon , Lina Issa (1) , Christine Joblin , Olga Kannavou (2) , Baria Khan , Ozan Lacinbala , David Languignon (4) , Romane Le Gal (6, 7) , Alexandros Maragkoudakis , Raphael Meshaka (4, 2) , Yoko Okada , Takashi Onaka , Sofia Pasquini , Marc W Pound , Massimo Robberto , Markus Röllig , Bethany Schefter , Thiébaut Schirmer (2) , Sílvia Vicente , Mark G Wolfire , Marion Zannese (2) , Isabel Aleman , Louis Allamandola , Rebecca Auchettl , Giuseppe Antonio Baratta , Salma Bejaoui , Partha P Bera , John H Black , François Boulanger (8) , Jordy Bouwman , Bernhard Brandl , Philippe Brechignac (5) , Sandra Brünken , Mridusmita Buragohain , Andrew Burkhardt , Alessandra Candian , Stéphanie Cazaux , Jose Cernicharo , Marin Chabot (9) , Shubhadip Chakraborty (10) , Jason Champion (1) , Sean W.J Colgan , Ilsa R Cooke , Audrey Coutens (1) , Nick L.J Cox (3) , Karine Demyk (1) , Jennifer Donovan Meyer , Sacha Foschino (1) , Pedro García-Lario , Lisseth Gavilan , Maryvonne Gerin (4) , Carl A Gottlieb , Pierre Guillard (11, 12) , Antoine Gusdorf (13, 4) , Patrick Hartigan , Jinhua He , Eric Herbst , Liv Hornekaer , Cornelia Jäger , Eduardo Janot-Pacheco , Michael Kaufman , Francisca Kemper , Sarah Kendrew , Maria S Kirsanova , Pamela Klaassen , Sun Kwok , Álvaro Labiano , Thomas S.-Y Lai , Timothy J Lee , Bertrand Lefloch (6) , Franck Le Petit (4) , Aigen Li , Hendrik Linz , Cameron J Mackie , Suzanne C Madden (14) , Joëlle Mascetti (15) , Brett A Mcguire , Pablo Merino , Elisabetta R Micelotta , Karl Misselt , Jon A Morse , Giacomo Mulas (1) , Naslim Neelamkodan , Ryou Ohsawa , Alain Omont (11) , Roberta Paladini , Maria Elisabetta Palumbo , Amit Pathak , Yvonne J Pendleton , Annemieke Petrignani , Thomas Pino (5) , Elena Puga , Naseem Rangwala , Mathias Rapacioli (16, 17) , Alessandra Ricca , Julia Roman-Duval , Joseph Roser , Evelyne Roueff (4) , Gaël Rouillé , Farid Salama , Dinalva A Sales , Karin Sandstrom , Peter Sarre , Ella Sciamma-O'Brien , Kris Sellgren , Sachindev S Shenoy , David Teyssier , Richard D Thomas , Aditya Togi , Laurent Verstraete (2) , Adolf N Witt , Alwyn Wootten , Henning Zettergren , Yong Zhang , Ziwei E Zhang , Junfeng Zhen
Ryan Chown
  • Function : Author
Ameek Sidhu
  • Function : Author
Els Peeters
  • Function : Author
Alexander G.G.M Tielens
  • Function : Author
Jan Cami
  • Function : Author
Felipe Alarcón
  • Function : Author
Dries van de Putte
  • Function : Author
Edwin A Bergin
  • Function : Author
Christiaan Boersma
  • Function : Author
Sara Cuadrado
  • Function : Author
Daniel Dicken
  • Function : Author
Asunción Fuente
  • Function : Author
Javier R Goicoechea
  • Function : Author
Karl D Gordon
  • Function : Author
Christine Joblin
  • Function : Author
Baria Khan
  • Function : Author
Ozan Lacinbala
  • Function : Author
Alexandros Maragkoudakis
  • Function : Author
Yoko Okada
  • Function : Author
Takashi Onaka
  • Function : Author
Sofia Pasquini
  • Function : Author
Marc W Pound
  • Function : Author
Massimo Robberto
  • Function : Author
Markus Röllig
  • Function : Author
Bethany Schefter
  • Function : Author
Sílvia Vicente
  • Function : Author
Mark G Wolfire
  • Function : Author
Isabel Aleman
  • Function : Author
Louis Allamandola
  • Function : Author
Rebecca Auchettl
  • Function : Author
Giuseppe Antonio Baratta
  • Function : Author
Salma Bejaoui
  • Function : Author
Partha P Bera
  • Function : Author
John H Black
  • Function : Author
Jordy Bouwman
  • Function : Author
Bernhard Brandl
  • Function : Author
Sandra Brünken
  • Function : Author
Mridusmita Buragohain
  • Function : Author
Andrew Burkhardt
  • Function : Author
Alessandra Candian
  • Function : Author
Stéphanie Cazaux
  • Function : Author
Jose Cernicharo
  • Function : Author
Sean W.J Colgan
  • Function : Author
Ilsa R Cooke
  • Function : Author
Jennifer Donovan Meyer
  • Function : Author
Pedro García-Lario
  • Function : Author
Lisseth Gavilan
  • Function : Author
Carl A Gottlieb
  • Function : Author
Patrick Hartigan
  • Function : Author
Jinhua He
  • Function : Author
Eric Herbst
  • Function : Author
Liv Hornekaer
  • Function : Author
Cornelia Jäger
  • Function : Author
Eduardo Janot-Pacheco
  • Function : Author
Michael Kaufman
  • Function : Author
Francisca Kemper
  • Function : Author
Sarah Kendrew
  • Function : Author
Maria S Kirsanova
  • Function : Author
Pamela Klaassen
  • Function : Author
Sun Kwok
  • Function : Author
Álvaro Labiano
  • Function : Author
Thomas S.-Y Lai
  • Function : Author
Timothy J Lee
  • Function : Author
Aigen Li
  • Function : Author
Hendrik Linz
  • Function : Author
Cameron J Mackie
  • Function : Author
Brett A Mcguire
  • Function : Author
Pablo Merino
  • Function : Author
Elisabetta R Micelotta
  • Function : Author
Karl Misselt
  • Function : Author
Jon A Morse
  • Function : Author
Naslim Neelamkodan
  • Function : Author
Ryou Ohsawa
  • Function : Author
Roberta Paladini
  • Function : Author
Maria Elisabetta Palumbo
  • Function : Author
Amit Pathak
  • Function : Author
Yvonne J Pendleton
  • Function : Author
Annemieke Petrignani
  • Function : Author
Elena Puga
  • Function : Author
Naseem Rangwala
  • Function : Author
Alessandra Ricca
  • Function : Author
Julia Roman-Duval
  • Function : Author
Joseph Roser
  • Function : Author
Gaël Rouillé
  • Function : Author
Farid Salama
  • Function : Author
Dinalva A Sales
  • Function : Author
Karin Sandstrom
  • Function : Author
Peter Sarre
  • Function : Author
Ella Sciamma-O'Brien
  • Function : Author
Kris Sellgren
  • Function : Author
Sachindev S Shenoy
  • Function : Author
David Teyssier
  • Function : Author
Richard D Thomas
  • Function : Author
Aditya Togi
  • Function : Author
Adolf N Witt
  • Function : Author
Alwyn Wootten
  • Function : Author
Henning Zettergren
  • Function : Author
Yong Zhang
  • Function : Author
Ziwei E Zhang
  • Function : Author
Junfeng Zhen
  • Function : Author

Abstract

Context. 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 µm. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. These high-quality data allow for an unprecedentedly detailed view of AIBs.Aims. 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 (i.e. the three H2 dissociation fronts), the atomic PDR, and the H II region.Methods. We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extracted five template spectra to represent the morphology and environment of the Orion Bar PDR. We investigated and characterised the AIBs in these template spectra. We describe the variations among them here.Results. 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. The Orion Bar spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 µm with well-defined profiles. In addition, the spectra display a wealth of weaker features and sub-components. The widths of many AIBs show clear and systematic variations, being narrowest in the atomic PDR template, but showing a clear broadening in the H II region template while the broadest bands are found in the three dissociation front templates. In addition, the relative strengths of AIB (sub-)components vary among the template spectra as well. All AIB profiles are characteristic of class A sources as designated by Peeters (2022, A&A, 390, 1089), except for the 11.2 µm AIB profile deep in the molecular zone, which belongs to class B11.2. Furthermore, the observations show that the sub-components that contribute to the 5.75, 7.7, and 11.2 µm AIBs become much weaker in the PDR surface layers. We attribute this to the presence of small, more labile carriers in the deeper PDR layers that are photolysed away in the harsh radiation field near the surface. The 3.3/11.2 AIB intensity ratio decreases by about 40% between the dissociation fronts and the H II region, indicating a shift in the polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs in the PDR surface layers, also likely due to the effects of photochemistry. The observed broadening of the bands in the molecular PDR is consistent with an enhanced importance of smaller PAHs since smaller PAHs attain a higher internal excitation energy at a fixed photon energy.Conclusions. Spectral-imaging observations of the Orion Bar using JWST yield key insights into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 µm AIB emission from class B11.2 in the molecular PDR to class A11.2 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’.Key words: astrochemistry / infrared: ISM / ISM: molecules / ISM: individual objects: Orion Bar / photon-dominated region (PDR) / techniques: spectroscopic★ The 5 template spectra are available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/685/A75★★ Tim Lee sadly passed away on Nov. 3, 2022.
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hal-04615526 , version 1 (18-06-2024)

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Ryan Chown, Ameek Sidhu, Els Peeters, Alexander G.G.M Tielens, Jan Cami, et al.. PDRs4All - IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar. Astron.Astrophys., 2024, 685, pp.A75. ⟨10.1051/0004-6361/202346662⟩. ⟨hal-04615526⟩
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