Orateur
Description
The 3D morphology of galaxies provides direct insights into the processes governing galaxy formation and evolution within the large-scale structures of the Universe. More precisely, the connection between the morphology of galaxies and halos is a key ingredient in cosmology and astrophysics. It is in particular interesting to understand the intrinsic alignments (IA) of galaxies, the correlation between the intrinsic 3D shapes of galaxies and the underlying tidal field of dark matter, which is known to be an astrophysical systematic effect for cosmic shear analyses. However, information about the 3D morphology of galaxies is lost along the line-of-sight due to the projection of the 3D shapes in 2D. In this talk, I present a novel method that I developed to infer the distribution of 3D galaxy shapes from their observed 2D images using simulation-based inference. I use halo catalogues of the N-body simulation AbacusSummit to extract the 3D shapes and 3D orientations of dark matter halos. Then, I use a Halo Occupation Distribution (HOD) model and galaxy clustering to populate these halos with galaxies. Finally, I present a forward model for the 3D shape of central galaxies that live inside these halos. I applied my method to the galaxy shape catalogue of the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), a multi-band optical survey which is going to cover 6250 deg^2 in the Northern sky. I obtain constraints on the distribution of 3D galaxy shapes and on the 3D galaxy-halo shape connection from 5800 deg^2 of observed sky. In future work, my idea is to predict an IA signal using this model of 3D morphology, in order to reveal, additionally to the observed galaxy alignments, extra information about the connection between the morphology of galaxies and halos in 3D.