X-ray Absorption Lines in the Warm-Hot Intergalactic Medium: Probing Chandra observations with the CAMEL simulations by Amanda Butler Contreras et al. on Wednesday 30 November

Known as the "Missing Baryon Problem", about one-third of baryons in the

local universe remain unaccounted for. The missing baryons are thought to

reside in the warm-hot intergalactic medium (WHIM) of the cosmic web filaments,

which are challenging to detect. Recent Chandra X-ray observations from

Kov\'acs et al. (2019) used a novel stacking analysis and detected an OVII

absorption line toward the sightline of a luminous quasar, hinting that the

missing baryons may reside in the WHIM. To explore how the properties of the

OVII absorption line depend on feedback physics, we compare the observational

results with predictions obtained from the Cosmology and Astrophysics with

MachinE Learning (CAMEL) Simulation suite. CAMELS consists of cosmological

simulations with state-of-the-art supernova (SN) and active galactic nuclei

(AGN) feedback models from the IllustrisTNG and SIMBA simulations, with varying

strengths. We find that the simulated OVII column densities are higher in the

outskirts of galaxies than in the large-scale WHIM, but they are consistently

lower than those obtained in the Chandra observations, for all feedback runs.

We establish that the OVII distribution is primarily sensitive to changes in

the SN feedback prescription, whereas changes in the AGN feedback prescription

have minimal impact. We also find significant differences in the OVII column

densities between the IllustrisTNG and SIMBA runs. We conclude that the tension

between the observed and simulated OVII column densities cannot be explained by

the wide range of feedback models implemented in CAMELS.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15675v1