Context:
The Euclid mission will provide weak lensing measurements with unprecedented precision, which have the potential to revolutionise our understanding of the Universe. However, as the statistical uncertainties decrease, controlling systematic effects becomes even more crucial. Among these, baryonic feedback, which redistributes gas within galaxies and clusters, remains one of the key astrophysical systematic effects limiting Euclid’s ability to constrain the equation of state of dark energy. Understanding baryonic feedback is one of the urgent challenges of cosmology today.

The thermal Sunyaev-Zel’dovich (tSZ) effect provides a unique window into the baryonic component of the Universe. This effect arises from the scattering of cosmic microwave background (CMB) photons by hot electrons in galaxy groups and clusters. This is the same hot gas that has been redistributed by baryonic feedback and is particularly relevant for weak lensing cosmology. The cross-correlation between tSZ and weak lensing (WL) probes how baryons trace and modify the cosmic structures, allowing joint constraints on cosmology and baryonic physics.

Most current tSZ-WL analyses rely on fitting angular power spectra under the assumption of a Gaussian likelihood. However, the tSZ signal is highly non-Gaussian, as it traces the massive structures of the Universe, and the power spectra fail to fully capture the information in the data. To unlock the scientific potential of the tSZ-WL analyses, it is essential to move beyond these simplifying assumptions.

PhD thesis:
The goal of this PhD project is to develop a novel simulation-based framework to jointly analyse tSZ and Euclid’s WL data. This framework will combine physically motivated forward models with advanced statistical and machine-learning techniques to provide accurate measurements of baryonic feedback and cosmological parameters. By jointly analysing tSZ and WL measurements, this project will increase the accuracy of Euclid’s cosmological analyses and improve our understanding of the dark matter-baryon connection.