PDRs4All V. Modelling the dust evolution across the illuminated edge of the Orion Bar
Journal article, 2024
Context. Interstellar dust particles, in particular carbonaceous nano-grains (like polycyclic aromatic hydrocarbons, fullerenes, and amorphous hydrogenated carbon), are critical players for the composition, energy budget, and dynamics of the interstellar medium (ISM). The dust properties, specifically the composition and size of dust grains are not static; instead, they exhibit considerable evolution triggered by variations in local physical conditions such as the density and gas temperature within the ISM, as is the case in photon-dominated regions (PDRs). The evolution of dust and its impact on the local physical and chemical conditions is thus a key question for understanding the first stages of star formation. Aims. From the extensive spectral and imaging data of the JWST PDRs4All program, we study the emission of dust grains within the Orion Bar – a well-known, highly far-UV (FUV)-irradiated PDR situated at the intersection between cold, dense molecular clouds, and warm ionized regions. The Orion Bar because of its edge-on geometry provides an exceptional benchmark for characterizing dust evolution and the associated driving processes under varying physical conditions. Our goal is to constrain the local properties of dust by comparing its emission to models. Taking advantage of the recent JWST data, in particular the spectroscopy of dust emission, we identify new constraints on dust and further previous works of dust modelling. Methods. To characterize interstellar dust across the Orion Bar, we follow its emission as traced by JWST NIRCam (at 3.35 and 4.8 µm) and MIRI (at 7.7, 11.3, 15.0, and 25.5 µm) broad band images, along with NIRSpec and MRS spectroscopic observations. First, we constrain the minimum size and hydrogen content of carbon nano-grains from a comparison between the observed dust emission spectra and the predictions of the Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS) coupled to the numerical code DustEM. Using this dust model, we then perform 3D radiative transfer simulations of dust emission with the SOC code (Scattering with OpenCL) and compare to data obtained along well chosen profiles across the Orion Bar. Results. The JWST data allows us, for the first time, to spatially resolve the steep variation of dust emission at the illuminated edge of the Orion Bar PDR. By considering a dust model with carbonaceous nano-grains and submicronic coated silicate grains, we derive unprecedented constraints on the properties of across the Orion Bar. To explain the observed emission profiles with our simulations, we find that the nano-grains must be strongly depleted with an abundance (relative to the gas) 15 times less than in the diffuse ISM. The NIRSpec and MRS spectroscopic observations reveal variations in the hydrogenation of the carbon nano-grains. The lowest hydrogenation levels are found in the vicinity of the illuminating stars suggesting photo-processing while more hydrogenated nano-grains are found in the cold and dense molecular region, potentially indicative of larger grains.
ISM: individual objects: Orion Bar
photon-dominated region (PDR)
infrared: ISM
Author
Meriem Elyajouri
Institut d'Astrophysique Spatiale
Nathalie Ysard
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Institut d'Astrophysique Spatiale
Alain Abergel
Institut d'Astrophysique Spatiale
Emilie Habart
Institut d'Astrophysique Spatiale
Laurent Verstraete
Institut d'Astrophysique Spatiale
A. Jones
Institut d'Astrophysique Spatiale
M. Juvela
University of Helsinki
Thiébaut-Antoine Schirmer
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Raphael Meshaka
Paris Observatory
Institut d'Astrophysique Spatiale
E. Dartois
University Paris-Saclay
J. Lebourlot
Paris Observatory
Gaël Rouillé
Friedrich Schiller University Jena
T. Onaka
University of Tokyo
Els Peeters
Western University
SETI Institute
O. Berné
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Felipe Alarcon
University of Maryland
J. Bernard-Salas
ACRI-ST
INCLASS Common Laboratory
Mridusmita Buragohain
University of Hyderabad
Jan Cami
Western University
SETI Institute
Amelie Canin
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Ryan Chown
Western University
K. Demyk
Institut de Recherche en Astrophysique et Planétologie (IRAP)
K. Gordon
Ghent university
Space Telescope Science Institute (STScI)
Olga Kannavou
Institut d'Astrophysique Spatiale
M. S. Kirsanova
Russian Academy of Sciences
S. C. Madden
University Paris-Saclay
R. Paladini
California Institute of Technology (Caltech)
Yvonne J. Pendleton
NASA Ames Research Center
Farid Salama
NASA Ames Research Center
Ilane Schroetter
Institut de Recherche en Astrophysique et Planétologie (IRAP)
Ameek Sidhu
Western University
M. Rollig
Physikalischer Verein
Goethe University Frankfurt
Boris Trahin
Institut d'Astrophysique Spatiale
Dries Van De Putte
Space Telescope Science Institute (STScI)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 685 A76Subject Categories
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/202348728