The Impact of the WHIM on the IGM Thermal State Determined from the Low- Lyman- Forest
arXiv:2308.14738
Abstract
At , shock heating caused by large-scale velocity flows and possibly violent feedback from galaxy formation, converts a significant fraction of the cool gas ( K) in the intergalactic medium (IGM) into warm-hot phase (WHIM) with K, resulting in a significant deviation from the previously tight power-law IGM temperature-density relationship, . This study explores the impact of the WHIM on measurements of the low- IGM thermal state, , based on the - distribution of the Lyman- forest. Exploiting a machine learning-enabled simulation-based inference method trained on Nyx hydrodynamical simulations, we demonstrate that [, ] can still be reliably measured from the - distribution at , 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 . The results suggest that the underlying of both simulations can be recovered with biases as low as dex, , 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 - distribution is not sensitive to the WHIM under realistic conditions. Finally, we investigate the physical properties of the detectable Lyman- absorbers, and discover that although their and distributions remain mostly unaffected by feedback, they are correlated with the photoionization rate used in the simulation.
23 pages, 24 figures