Guilhem Lavaux is a permanent CNRS research director at the Institut d’Astrophysique de Paris. Before this, he was a CITA National Fellow at the University of Waterloo and Associate postdoctoral researcher at the Perimeter Institute for Theoretical Physics. He works on modelling of the dynamics of the Universe, the exploration of new statistical tools to constrain cosmological parameters.
Title: From Galaxy Catalogs to the Initial Conditions: Building a Digital Twin of the Nearby Universe
Abstract: In our current cosmological paradigm, every observable structure, from the Milky Way to massive galaxy clusters, grew from a specific realization of primordial gravitational-potential fluctuations. Can we infer the realization that gave rise to the galaxies we observe? And can we evolve it forward to obtain a physical "digital twin" of our cosmic neighborhood?
Modern surveys, including Rubin-LSST, Euclid and DESI, are now mapping millions to billions of galaxies. However, cosmological analyses still rely mostly on two-point statistics, discarding much of the small-scale information. Field-level inference, developed over the past fifteen years, follows a different route: it forward-models the full three-dimensional galaxy field and samples the primordial fluctuations directly.
In this talk, I will present the Manticore digital twins, inferred with the BORG (Bayesian Origin Reconstruction from Galaxies) framework. Manticore-Local is built from the 2M++ galaxy compilation. Manticore-Deep adds the Sloan Digital Sky Survey (SDSS) to reach redshift 0.7 in a 4 Gpc/h box. A Local Group sibling focuses on the Milky Way and M31. I will first explain what goes into these reconstructions and where the models fall short. I will then show how we validate the twins against independent data, such as cluster masses and galaxy distances. Finally, I will discuss the new answers and new problems emerging from them: the impact on local measurements of the Hubble constant, the mass of the Local Group, and new challenges for the subgrid models of hydrodynamical simulations such as the FLAMINGO suite.