Numerical simulations of the Warm-Hot Intergalactic Medium

TL;DR

This paper reviews numerical simulation predictions for the warm-hot intergalactic medium (WHIM), its origin, properties, and observability, highlighting current limitations and future detection prospects with upcoming X-ray missions.

Contribution

It provides a comprehensive review of the current state of numerical simulations of the WHIM and discusses future observational strategies with next-generation X-ray telescopes.

Findings

WHIM contains up to 50% of baryons at z~0

Current X-ray telescopes lack sensitivity to detect the hotter WHIM

Future missions may detect emission and absorption lines from highly ionised atoms

Abstract

In this paper we review the current predictions of numerical simulations for the origin and observability of the warm hot intergalactic medium (WHIM), the diffuse gas that contains up to 50 per cent of the baryons at z~0. During structure formation, gravitational accretion shocks emerging from collapsing regions gradually heat the intergalactic medium (IGM) to temperatures in the range T~10^5-10^7 K. The WHIM is predicted to radiate most of its energy in the ultraviolet (UV) and X-ray bands and to contribute a significant fraction of the soft X-ray background emission. While O VI and C IV absorption systems arising in the cooler fraction of the WHIM with T~10^5-10^5.5 K are seen in FUSE and HST observations, models agree that current X-ray telescopes such as Chandra and XMM-Newton do not have enough sensitivity to detect the hotter WHIM. However, future missions such as Constellation-X and XEUS might be able to detect both emission lines and absorption systems from highly ionised atoms such as O VII, O VIII and Fe XVII.