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arXiv · 2110.01628

The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies

Enrico Garaldi·Rahul Kannan·Aaron Smith·Volker Springel·Rüdiger Pakmor·Mark Vogelsberger·Lars Hernquist
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Abstract

The high-redshift intergalactic medium (IGM) and the primeval galaxy population are rapidly becoming the new frontier of extra-galactic astronomy. We investigate the IGM properties and their connection to galaxies at $z\geq5.5$ under different assumptions for the ionizing photon escape and the nature of dark matter, employing our novel THESAN radiation-hydrodynamical simulation suite, designed to provide a comprehensive picture of the emergence of galaxies in a full reionization context. Our simulations have realistic `late' reionization histories, match available constraints on global IGM properties and reproduce the recently-observed rapid evolution of the mean free path of ionizing photons. We additionally examine high-z Lyman-$\alpha$ transmission. The optical depth evolution is consistent with data, and its distribution suggests an even-later reionization than simulated, although with a strong sensitivity to the source model. We show that the effects of these two unknowns can be disentangled by characterising the spectral shape and separation of Lyman-$\alpha$ transmission regions, opening up the possibility to observationally constrain both. For the first time in simulations, THESAN reproduces the modulation of the Lyman-$\alpha$ flux as a function of galaxy distance, demonstrating the power of coupling a realistic galaxy formation model with proper radiation-hydrodynamics. We find this feature to be extremely sensitive on the timing of reionization, while being relatively insensitive to the source model. Overall, THESAN produces a realistic IGM and galaxy population, providing a robust framework for future analysis of the high-z Universe.

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Enrico Garaldi, Rahul Kannan, Aaron Smith, Volker Springel, Rüdiger Pakmor, Mark Vogelsberger, Lars Hernquist. 2021-10-04. The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies. https://doi.org/10.1093/mnras%2Fstac257

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