OH As A Probe Of The Warm Water Cycle In Planet-forming Disks

By Keith Cowing
Status Report
December 22, 2023
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OH As A Probe Of The Warm Water Cycle In Planet-forming Disks
JWST NIRCam composite image of the Orion Bar, located in the Orion molecular cloud. Red is the 3.35µm emission (F335M NIRCam filter), blue is the emission of Paα (F187N filter subtracted by F182M filter) and green is the emission of the H2 0-0 S(9) line at 4.70 µm (F470N filter subtracted by F480M filter). The inset shows a zoom-in of the d203-506 planet-forming disk where OH lines are detected. Red is the emission of the H2 1-0 S(1) line at 2.12 µm (F212N filter), blue is the [FeII] line emission at 1.64 µm (F164N filter), and green is the emission in the F140M broad-band near-IR filter that traces scattered light around 1.4 µm (F140M broad band filter). The white contours represent the emission of the OH rotational line at 9.79 µm detected with MIRI-MRS (levels are 1.1, 2.5 ×10−5 erg cm−2 s −1 sr−1 ). The bright spot in the northwestern part of the envelope coincides with the region of interaction between a jet and the photoevaporative wind. The brightest OH emission originates from here. The spectra shown in Fig. 2 and 3 are an average over the region delineated by the green circle in order to have the best S/N. Image credits: NASA, ESA, CSA, PDRs4All ERS Team, — astro-ph.EP

Water is a key ingredient for the emergence of life as we know it. Yet, its destruction and reformation in space remains unprobed in warm gas.

Here, we detect the hydroxyl radical (OH) emission from a planet-forming disk exposed to external far-ultraviolet (FUV) radiation with the James Webb Space Telescope. The observations are confronted with the results of quantum dynamical calculations.

The highly excited OH infrared rotational lines are the tell-tale signs of H2O destruction by FUV. The OH infrared ro-vibrational lines are attributed to chemical excitation via the key reaction O+H=OH+H which seeds the formation of water in the gas-phase. We infer that the equivalent of the Earth ocean’s worth of water is destroyed per month and replenished.

These results show that under warm and irradiated conditions water is destroyed and efficiently reformed via gas-phase reactions. This process, assisted by diffusive transport, could reduce the HDO/H2O ratio in the warm regions of planet-forming disks.

Marion Zannese, Benoît Tabone, Emilie Habart, Javier R. Goicoechea, Alexandre Zanchet, Ewine F. van Dishoeck, Marc C. van Hemert, John H. Black, Alexander G. G. M. Tielens, A. Veselinova, P. G. Jambrina, M. Menendez, E. Verdasco, F. J. Aoiz, L. Gonzalez-Sanchez, Boris Trahin, Emmanuel Dartois, Olivier Berné, Els Peeters, Jinhua He, Ameek Sidhu, Ryan Chown, Ilane Schroetter, Dries Van De Putte, Amélie Canin, Felipe Alarcón, Alain Abergel, Edwin A. Bergin, Jeronimo Bernard-Salas, Christiaan Boersma, Emeric Bron, Jan Cami, Daniel Dicken, Meriem Elyajouri, Asunción Fuente, Karl D. Gordon, Lina Issa, Christine Joblin, Olga Kannavou, Baria Khan, Ozan Lacinbala, David Languignon, Romane Le Gal, Alexandros Maragkoudakis, Raphael Meshaka, Yoko Okada, Takashi Onaka, Sofia Pasquini, Marc W. Pound, Massimo Robberto, Markus Röllig, Bethany Schefter, Thiébaut Schirmer, Sílvia Vicente, Mark G. Wolfire

Comments: Version submitted to Nature Astronomy
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2312.14056 [astro-ph.EP] (or arXiv:2312.14056v1 [astro-ph.EP] for this version)
Submission history
From: Marion Zannese
[v1] Thu, 21 Dec 2023 17:32:23 UTC (37,043 KB)
Astrobiology, Astrochemistry

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻