Numerical Simulations of the Warm-Hot Intergalactic Medium

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 Hubble Space Telescope 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.

A semi-analytic model for the co-evolution of galaxies, black holes and active galactic nuclei

“…These two components (warm/hot diffuse gas and hot gas in haloes) dominate the baryon budget at all redshifts, in agreement with observational constraints at low redshift (e.g. Fukugita & Peebles 2004) and the predictions of numerical hydrodynamic simulations (Bertone, Schaye & Dolag 2008, and references therein). Finally, we show the baryons in cold gas in galactic discs, in stars in the discs and bulges of galaxies and in DSHs around galaxies.…”

“…We analyse the redshift‐dependent breakdown of all the baryons in our fiducial model into each of the various components that we track: hot gas in haloes, warm/hot diffuse gas in the IGM, cold gas in galactic discs, stars in galaxies and stars in DSHs. We find that hot gas in haloes and warm/hot gas in the IGM dominate at all redshifts, in agreement with the predictions of numerical cosmological simulations (Bertone et al 2008, and references therein) and with the observational baryon census at low redshift (Fukugita & Peebles 2004). Therefore, in order to produce more cold gas at high redshift, we either require more efficient cooling of hot gas or less efficient reheating and ejection of cold gas by SN feedback.…”

The effect of photoionization on the cooling rates of enriched, astrophysical plasmas

“…Because the cooling of the WHIM tends to be dominated by line radiation, its density is low (δ∼ 10– 10 2 ; e.g. Bertone, Schaye & Dolag 2008) and the WHIM gas may well be enriched to values of 10 per cent of solar or higher, both metals and photoionization by the UV background may be important. Fig.…”

Turbulence modeling and the physics of the intra-cluster medium

“…Furthermore, it will be also important to explore the turbulent flow not only in the ICM, but also in the cluster outskirts and in the cosmic web. The knowledge of the turbulent state of this gas is potentially important for shaping the emission and absorption lines associated with the WarmHot Intergalactic Medium (see [46] for a review). From a computational viewpoint, numerical improvements in the FEARLESS scheme are ongoing [47], in order to better account for complex flows with large density gradients.…”