The Impact of the WHIM on the IGM Thermal State Determined from the Low-z Lyman-α Forest

2023/08/28 by Teng Hu, Vikram Khaire, Hu, Teng +11 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Scientific Research and Discoveries

paper · pdf · doi:10.48550/arxiv.2308.14738

openalex publication_date 2023/08/28 · openalex created_date 2023/08/31 · openalex updated_date 2026/07/28

Abstract

At z \lesssim 1, shock heating caused by large-scale velocity flows and possibly violent feedback from galaxy formation, converts a significant fraction of the cool gas (T∼ 10⁴ K) in the intergalactic medium (IGM) into warm-hot phase (WHIM) with T >10⁵K, resulting in a significant deviation from the previously tight power-law IGM temperature-density relationship, T=T₀ (ρ/ ρ)^γ-1. This study explores the impact of the WHIM on measurements of the low-z IGM thermal state, [T₀,γ], based on the b-N_{H I} distribution of the Lyman-α forest. Exploiting a machine learning-enabled simulation-based inference method trained on Nyx hydrodynamical simulations, we demonstrate that [T₀, γ] can still be reliably measured from the b-N_{H I} distribution at z=0.1, notwithstanding the substantial WHIM in the IGM. To investigate the effects of different feedback, we apply this inference methodology to mock spectra derived from the IllustrisTNG and Illustris simulations at z=0.1. The results suggest that the underlying [T₀,γ] of both simulations can be recovered with biases as low as |Δlog(T₀/K)| \lesssim 0.05 dex, |Δγ| \lesssim 0.1, smaller than the precision of a typical measurement. Given the large differences in the volume-weighted WHIM fractions between the three simulations (Illustris 38%, IllustrisTNG 10%, Nyx 4%) we conclude that the b-N_{H I} distribution is not sensitive to the WHIM under realistic conditions. Finally, we investigate the physical properties of the detectable Lyman-α absorbers, and discover that although their T and Δ distributions remain mostly unaffected by feedback, they are correlated with the photoionization rate used in the simulation.

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• Discovery of Weak O VI Absorption in Underdense Regions of the Low-Redshift Intergalactic Medium

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