Inferring the Thermal History of the Intergalactic Medium from the Lyman-alpha Forest

Prof. Brant Robertson (UC Santa Cruz)
Tuesday, March 15, 2022 - 11:00am

The filamentary network of intergalactic medium (IGM) gas that gives origin to the "Lyman-α forest" encodes information on the physics of structure formation and the early thermodynamics of diffuse baryonic material. I will present results from a massive suite of hundreds of high-resolution cosmological hydrodynamical simulations run with the Graphics Processing Unit-accelerated code Cholla to study the IGM at high spatial resolution. By varying the amplitude and timing of the photoheating and photoionizing background produced by star-forming galaxies and active galactic nuclei, we can match the observed hydrogen Lyman-alpha forest power spectra and helium Lyman-alpha forest opacity. The available data tightly constrain the photoionization and photoheating history of the IGM, and allow us to infer its thermal history. I will discuss how our results can help reveal the timing and the sources of hydrogen and helium reionization, and how we can constrain cosmological physics from the Lyman-α forest while robustly accounting for thermal structure of the IGM.

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