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Astronomy Colloquium - Simeon Bird

Photon passing through the large scale structure of the universe
October 23, 2025
3:00 pm - 4:00 pm
Hybrid: Chem & Biomolecular Eng & Chem (CBEC) - Room 130 and Zoom

Title: An S8 tension at redshift 3: Lyman alpha forest cosmology from the PRIYA simulations

Speaker: Simeon Bird (UC Riverside)

Abstract:

I will talk about our recent work building a new simulation suite, emulator and likelihood to make cosmological parameter constraints from the eBOSS Lyman-alpha forest, absorption from neutral hydrogen gas spread throughout the intergalactic medium. The PRIYA simulations are a large suite of cosmological hydrodynamic simulations, with 60 different cosmologies combining a large box, high resolution and a state of the art galaxy formation model. Using them we found that the Lyman-alpha forest prefers a low amplitude of matter clustering, mirroring the S8 tension seen in weak lensing surveys at z=3, where AGN feedback effects are expected to be weak.

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