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.

infrared: ISM

ISM: individual objects: Orion Bar

photon-dominated region (PDR)

Author

Meriem Elyajouri

Institut d'Astrophysique Spatiale

Nathalie Ysard

Institut d'Astrophysique Spatiale

Institut de Recherche en Astrophysique et Planétologie (IRAP)

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

SETI Institute

Western University

O. Berné

Institut de Recherche en Astrophysique et Planétologie (IRAP)

Felipe Alarcon

University of Maryland

J. Bernard-Salas

Innovative Common Laboratory For Space Spectroscopy (INCLASS)

ACRI-ST

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

Space Telescope Science Institute (STScI)

Ghent university

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 A76

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/202348728

More information

Latest update

8/19/2024