PDRs4All
Authors: Habart Emilie , Peeters Els , Berné Olivier , Trahin Boris , Canin Amélie , Chown Ryan , Sidhu Ameek , Van De Putte Dries , Alarcón Felipe , Schroetter Ilane , Dartois Emmanuel , Vicente Sílvia , Abergel Alain , Bergin Edwin A. , Bernard-Salas Jeronimo , Boersma Christiaan , Bron Emeric , Cami Jan , Cuadrado Sara , Dicken Daniel , Elyajouri Meriem , Fuente Asunción , Goicoechea Javier R. , Gordon Karl D. , Issa Lina , Joblin Christine , Kannavou Olga , Khan Baria , Lacinbala Ozan , Languignon David , Le Gal Romane , Maragkoudakis Alexandros , Meshaka Raphael , Okada Yoko , Onaka Takashi , Pasquini Sofia , Pound Marc W. , Robberto Massimo , Röllig Markus , Schefter Bethany , Schirmer Thiébaut , Tabone Benoit , Tielens Alexander G. G. M. , Wolfire Mark G. , Zannese Marion , Ysard Nathalie , Miville-Deschenes Marc-Antoine , Aleman Isabel , Allamandola Louis , Auchettl Rebecca , Baratta Giuseppe Antonio , Bejaoui Salma , Bera Partha P. , Black John H. , Boulanger Francois , Bouwman Jordy , Brandl Bernhard , Brechignac Philippe , Brünken Sandra , Buragohain Mridusmita , Burkhardt Andrew , Candian Alessandra , Cazaux Stéphanie , Cernicharo Jose , Chabot Marin , Chakraborty Shubhadip , Champion Jason , Colgan Sean W. J. , Cooke Ilsa R. , Coutens Audrey , Cox Nick L.J. , Demyk Karine , Meyer Jennifer Donovan , Foschino Sacha , García-Lario Pedro , Gavilan Lisseth , Gerin Maryvonne , Gottlieb Carl A. , Guillard Pierre , Gusdorf Antoine , Hartigan Patrick , He Jinhua , Herbst Eric , Hornekaer Liv , Jäger Cornelia , Janot-Pacheco Eduardo , Kaufman Michael , Kemper Francisca , Kendrew Sarah , Kirsanova Maria S. , Klaassen Pamela , Kwok Sun , Labiano Álvaro , Lai Thomas S.-Y. , Lee Timothy J. , Lefloch Bertrand , Le Petit Franck , Li Aigen , Linz Hendrik , Mackie Cameron J. , Madden Suzanne C. , Mascetti Joëlle , McGuire Brett A. , Merino Pablo , Micelotta Elisabetta R. , Misselt Karl , Morse Jon A. , Mulas Giacomo , Neelamkodan Naslim , Ohsawa Ryou , Omont Alain , Paladini Roberta , Palumbo Maria Elisabetta , Pathak Amit , Pendleton Yvonne J. , Petrignani Annemieke , Pino Thomas , Puga Elena , Rangwala Naseem , Rapacioli Mathias , Ricca Alessandra , Roman-Duval Julia , Roser Joseph , Roueff Evelyne , Rouillé Gaël , Salama Farid , Sales Dinalva A. , Sandstrom Karin , Sarre Peter , Sciamma-O’Brien Ella , Sellgren Kris , Shenoy Sachindev S. , Teyssier David , Thomas Richard D. , Togi Aditya , Verstraete Laurent , Witt Adolf N. , Wootten Alwyn , Zettergren Henning , Zhang Yong , Zhang Ziwei E. , Zhen Junfeng 
Published: September 2023

Context. TheJames WebbSpace Telescope (JWST) has captured the most detailed and sharpest infrared (IR) images ever taken of the inner region of the Orion Nebula, the nearest massive star formation region, and a prototypical highly irradiated dense photo-dissociation region (PDR).

Aims. We investigate the fundamental interaction of far-ultraviolet (FUV) photons with molecular clouds. The transitions across the ionization front (IF), dissociation front (DF), and the molecular cloud are studied at high-angular resolution. These transitions are relevant to understanding the effects of radiative feedback from massive stars and the dominant physical and chemical processes that lead to the IR emission that JWST will detect in many Galactic and extragalactic environments.

Methods. We utilized NIRCam and MIRI to obtain sub-arcsecond images over ~150″ and 42″ in key gas phase lines (e.g., Paα, Brα, [FeII] 1.64 µm, H21−0 S(1) 2.12 µm, 0–0 S(9) 4.69 µm), aromatic and aliphatic infrared bands (aromatic infrared bands at 3.3–3.4 µm, 7.7, and 11.3 µm), dust emission, and scattered light. Their emission are powerful tracers of the IF and DF, FUV radiation field and density distribution. Using NIRSpec observations the fractional contributions of lines, AIBs, and continuum emission to our NIRCam images were estimated. A very good agreement is found for the distribution and intensity of lines and AIBs between the NIRCam and NIRSpec observations.

Results. Due to the proximity of the Orion Nebula and the unprecedented angular resolution of JWST, these data reveal that the molecular cloud borders are hyper structured at small angular scales of ~0.1–1″ (~0.0002–0.002 pc or ~40–400 au at 414 pc). A diverse set of features are observed such as ridges, waves, globules and photoevaporated protoplanetary disks. At the PDR atomic to molecular transition, several bright features are detected that are associated with the highly irradiated surroundings of the dense molecular condensations and embedded young star. Toward the Orion Bar PDR, a highly sculpted interface is detected with sharp edges and density increases near the IF and DF. This was predicted by previous modeling studies, but the fronts were unresolved in most tracers. The spatial distribution of the AIBs reveals that the PDR edge is steep and is followed by an extensive warm atomic layer up to the DF with multiple ridges. A complex, structured, and folded H0/H2DF surface was traced by the H2lines. This dataset was used to revisit the commonly adopted 2D PDR structure of the Orion Bar as our observations show that a 3D “terraced” geometry is required to explain the JWST observations. JWST provides us with a complete view of the PDR, all the way from the PDR edge to the substructured dense region, and this allowed us to determine, in detail, where the emission of the atomic and molecular lines, aromatic bands, and dust originate.

Conclusions. This study offers an unprecedented dataset to benchmark and transform PDR physico-chemical and dynamical models for the JWST era. A fundamental step forward in our understanding of the interaction of FUV photons with molecular clouds and the role of FUV irradiation along the star formation sequence is provided.