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Toward precision cosmology with the Lya forest

Neutral hydrogen in the Intergalactic Medium produces a collection of Lya absorptions, called the Lya forest, seen in the spectra of background objects. According to the common paradigm, neutral hydrogen in the IGM evolves from primordial density fluctuations in a low density and photo-ionized environment. It, therefore, acts as a direct tracer of Dark Matter (DM). However, it also implies that temperature and density are tightly coupled, giving rise to degeneracies between parameters describing either cosmology or the IGM thermal history. The Lya forest 1D power spectrum is sensitive to clustering on small scales, and as such to the smoothing scale of relativistic particles. It has been used to put the strongest constraints on the sum of the neutrino masses and to study DM models. To infer cosmological constraints and to test our models at the percent level accuracy, the measurements need to be compared to state-of-the-art hydrodynamical simulations. We also need to refine our understanding of the impact of galactic feedbacks on the IGM temperature.

I will present the analysis that leads to the most recent P1D measurement. As the current uncertainties are at the percent level, and will even shrink further in the DESI era, the P1D becomes sensitive to complex mechanical effects known as AGN feedback. We use Adaptative Mesh Refinement (AMR) hydrodynamical simulations, the Horizon-AGN and Horizon-noAGN simulations, to evaluate its impact on the P1D and prevent degeneracies with neutrino effects. Finally, I will present current constraints on the mass of active neutrinos and on Warm Dark Matter models.

Speaker: Solene Chabanier, Universite Paris-Saclay

Room LBL 50-5132

Friday, 11/08/19


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Lawrence Berkeley National Laboratory

1 Cyclotron Road
Berkeley, CA 94720

Website: Click to Visit