The Euclid mission will deliver weak lensing data with unprecedented precision, which has the potential to revolutionise our understanding of dark energy and the growth of cosmic structures. Extracting its full information content requires going beyond the standard analyses. To make optimal use of the data, the OCAPi project will analyse Euclid's lensing maps directly at the pixel level. This approach, known as field-level inference, captures all the information and provides up to 5 times better constraints on the cosmological parameters (Porqueres et al. 2022, 2023).

This increased precision, however, requires an accurate modelling of the data. One of the main calibration challenges in weak lensing surveys is the redshift distribution of the lensed galaxies. Current calibration methods were designed for the standard analyses and may not be sufficiently accurate for field-level techniques. Quantifying the accuracy requirements and developing methods capable of reaching it is essential to enable field-level analyses of Euclid data and unlock the full scientific potential of the survey.

The goal of this PhD project is to develop a new redshift sampler for weak lensing, designed to meet the accuracy requirements of field-level inference. This sampler will combine physical models of galaxy populations with flexible machine-learning techniques. The thesis will contribute to maximising the potential of Euclid's weak lensing data and advance our understanding of the formation of cosmic structures.

The James Webb Space Telescope is revolutionizing our understanding of the distant universe. A result has emerged that challenges our models: the extremely high efficiency of star formation in distant galaxies. However, this finding is derived indirectly: we measure the mass of stars in galaxies, not their star formation rate. This is the main weakness of the James Webb. The aim of this thesis is to remedy this weakness by using its angular resolution capacity, which has not been taken into account until now, in order to obtain a more robust measurement of the SFR of distant galaxies. We will deduce a law that will improve the robustness of SFR determination using morphological properties and combining data from the James Webb Space Telescope with data from ALMA (z=1-3). We will then apply it to the distant universe (z=3-6, part 2) and use it as a benchmark for numerical simulations (part 3).

Aurorae are well known optical phenomena in the Solar System planets. Aurorae have great diagnostic value, as their emissions reveal the planets’ atmospheric compositions, the occurrence of magnetic fields and the solar wind conditions at the planet’s orbit. Looking for aurorae on exoplanets and brown dwarfs is the next frontier. A first breakthrough in this direction has occurred recently, with the detection of a CH4 emission attributed to auroral excitation on the brown dwarf W1935. This detection, and the prospects of observing other auroral features with existent and upcoming telescopes, is what motivates this project. In particular, we will build the first model dedicated to investigate CH4 and H3+ auroral emission on exoplanets and brown dwarfs. The model will be used to investigate the conditions at W1935, and to predict the detectability of aurorae on other sub-stellar objects.

One of JWST’s major goals is to characterize, for the first time, the atmospheres of rocky, temperate exoplanets, a key milestone in the search for potentially habitable worlds. The temperate rocky exoplanets accessible to JWST are primarily those orbiting M-type stars. However, a major question remains regarding the ability of planets orbiting M-dwarfs to retain their atmospheres.
In 2024, an exceptional 500-hour Director’s Discretionary Time (DDT) program, entitled Rocky Worlds, was dedicated to this topic, underlining its strategic importance at the highest level (NASA, STScI).
The main objective of this PhD project is to: 1) Analyze all available JWST/MIRI eclipse data for rocky exoplanets from Rocky Worlds and other public programs using a consistent and homogeneous framework; 2)Search for population-level trends in the observations and interpret them using 3D atmospheric simulations.
Through this work, we aim to identify the physical processes that control the presence and composition of atmospheres on temperate rocky exoplanets.

This PhD project aims to better understand interstellar medium turbulence, a key phenomenon governing the formation of stars and galactic structures. This turbulence—magnetized, supersonic, and multiphase—influences how energy is transferred and dissipated, thereby regulating the efficiency of star formation throughout the history of the Universe. Its study is complex, as it involves a wide range of spatial and temporal scales that are difficult to reproduce numerically. Advances in high-performance computing, particularly the advent of GPU-based exascale supercomputers, now make it possible to perform much more refined simulations.

The Dyablo code, developed at IRFU, will be used to carry out large-scale three-dimensional simulations with adaptive mesh refinement to resolve the regions where energy dissipation occurs. The study will progress in stages: first, simulations of simple isothermal flows will be conducted, followed by models that include heating, cooling, magnetic fields, and gravity. The turbulent properties will be analyzed using power spectra, structure functions, and density distributions, in order to better understand the formation of dense regions that give birth to stars. Finally, the work will be extended to the galactic scale, in collaboration with other French institutes, to investigate the large-scale energy cascade of turbulence across entire galaxies.

This PhD project focuses on achieving unbiased measurements of weak gravitational lensing — the tiny distortions in galaxy shapes caused by the matter along the line of sight. This technique is key to studying dark matter, dark energy, and gravity, and lies at the heart of the Euclid space mission launched in 2023. Traditional shape-measurement methods introduce systematic biases in shear estimation. The goal of this PhD is to develop and extend an innovative forward-modelling approach that directly infers the shear by simulating realistic galaxy images using deep-learning architectures. The student will adapt this framework to real Euclid data, accounting for the complexity of the Science Ground Segment (SGS) and implementing GPU-accelerated and high-performance computing solutions to scale to the full sky coverage. The project is timely, coinciding with Euclid’s first public data release in 2026. The expected outcome is a more accurate and robust shear estimation method, enabling the next generation of precision cosmology analyses.

Gamma-Ray Bursts (GRB) are the most powerful explosions in the Universe. They last a few tens of seconds and emit the same amount of energy as the Sun during its entire lifetime. They gamma-ray emission is followed by a long lasting (hours to days) emission from the X-rays to the radio band. This "afterglow" emission is rich on information about the GRB nearby environnent and host galaxy. SVOM (Space based astronomical Variable Object Monitor) is a Sino-French mission, dedicated to GRB studies, and has been successfully launched in June 2024. It carries a multi-wavelength payload covering gamma-rays/X-rays/optical and includes two dedicated ground based robotic telescopes in Mexico and China.
The PHD project is focussed on the exploitation of the SVOM data for GRBs. The successful candidate will join the MXT science Teal at DAp. MXT is a new type of X-ray telescope, for which the DAp is responsible and its Instrument Centre is also hosted at DAp.
The PHD student will participate actively to the spectral and temporal analysis of MXT data. These data will be compared
to the other data acquired by the SVOM collaboration, especially in the optical an infrared domains.
This dataset will be used as a support to the physical interpretation of GRBs. More specifically, the aspects related to the modeling of the energy injection in the first phases of the afterglow will be used to determine the nature of the compact object at the origin of the relativistic flux, generating the electromagnetic emission observed.