ED Sciences Physiques et de l'Ingénieur
Molecular composition of planetary formation regions by tomographic observations and chemistry modeling.
by Coralie FOUCHER (Laboratoire d'Astrophysique de Bordeaux)
The defense will take place at 10h00 - Salle Univers All. Geoffroy Saint-Hilaire, 33600 Pessac
in front of the jury composed of
- Anne DUTREY - Directrice de recherche - Université de Bordeaux - Directeur de these
- Anaëlle MAURY - Professeure - Institut de Ciències de l'Espai (CSIC - ICE) - Rapporteur
- Audrey COUTENS - Astronome adjoint - Institut de Recherche en Astrophysique et Planétologie (IRAP) - Rapporteur
- Sean RAYMOND - Directeur de recherche - Laboratoire d'Astrophysique de Bordeaux (LAB) - Examinateur
- Marion VILLENAVE - Chargée de recherche - Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) - Examinateur
Protoplanetary disks, rotating structures of gas and dust surrounding young stars, are the birthplaces of planet formation. Understanding their physical and chemical structure, both radially and vertically, is a major challenge in modern astrophysics. High-resolution interferometric surveys conducted with ALMA have revealed remarkable radial substructures such as rings, gaps, and spirals in disks observed at moderate inclinations (30°–60°). In contrast, the vertical structure of these objects remains difficult to constrain observationally. In this context, edge-on disks provide a unique opportunity. Their orientation allows the vertical stratification of gas and dust to be probed directly, without the geometrical degeneracies inherent to moderately inclined systems. These objects therefore constitute ideal laboratories for accessing the emission heights of molecular tracers and studying physico-chemical conditions as a function of altitude within the disk. This thesis aims to precisely characterize the physical and chemical conditions, such as density and temperature, as a function of height within the disk, in order to better understand the environment of planet formation. To achieve this, I combine two complementary approaches: the molecular tomography method (Dutrey et al. 2017), which enables a direct determination of the radial and vertical structure from interferometric observations, and the parametric radiative transfer code DiskFit (Piétu et al. 2007), which models disk emission and constrains its physical properties through χ² minimization in the Fourier plane. This analysis is based on a multi-molecular dataset obtained through ALMA observations, complemented by new observations from NOEMA. The first part of this thesis focuses on the edge-on disk SSTTau042021 (Foucher et al. 2025 and Foucher et al. 2026, in prep.). The results reveal a vertically extended gaseous structure, with strong molecular stratification between a cold midplane and a warmer disk atmosphere. Some molecular tracers also indicate the presence of material above the disk, possibly associated with a disk wind. In addition, gas is detected beyond the outer radius of the dust disk, indicating a gaseous component more extended than the continuum emission. These observations therefore provide direct constraints on the thermal structure and mass distribution of the disk. The second part focuses on the edge-on disk Flying Saucer. In addition to combining molecular tomography and physical modeling with DiskFit (Guilloteau et al. 2025 & Dutrey et al. 2025), an approach was developed to investigate the link between physical and chemical structure using astrochemical simulations performed with the Nautilus code within the framework of the thesis of Sacha Gavino (Gavino et al. 2021). These simulations were coupled with radiative transfer calculations carried out using RADMC-3D in order to produce synthetic emission maps. The simulated observations were then compared with real data through tomographic reconstruction, enabling a direct comparison between the vertical chemical stratification predicted by the models and the observed emission. Finally, the last part aims to place these two sources into a broader context by studying the dependence of radial and vertical structures on the properties of the disk and the central star. Preliminary results are presented for two additional edge-on disks: CB26, observed with new NOEMA data, and Gomez's Hamburger, analyzed within the framework of the ALMA project 2022.1.00269.S.