The effect of feedback on the emission properties of the Warm-Hot Intergalactic Medium

TL;DR

This study uses cosmological simulations to analyze how feedback mechanisms like galactic winds influence the X-ray emission of the Warm-Hot Intergalactic Medium, affecting observable signals and the unresolved X-ray background.

Contribution

It provides new insights into the impact of galactic winds and other feedback processes on the emission properties of the WHIM using detailed hydrodynamical simulations.

Findings

Galactic winds double the emission from galaxy clusters and WHIM.

Oxygen line emission increases threefold due to galactic winds and 20% with a top-heavy IMF.

Faint groups and WHIM may account for half to all of the unresolved X-ray background.

Abstract

At present, 30-40 per cent of the baryons in the local Universe is still undetected. According to theoretical predictions, this gas should reside in filaments filling the large-scale structure (LSS) in the form of a Warm-Hot Intergalactic Medium (WHIM), at temperatures of 10^5 - 10^7 K, thus emitting in the soft X-ray energies via free-free interaction and line emission from heavy elements. In this work we characterize the properties of the X-ray emission of the WHIM, and the LSS in general, focusing on the influence of different physical mechanisms, namely galactic winds (GWs), black-hole feedback and star-formation, and providing estimates of possible observational constraints. To this purpose we use a set of cosmological hydrodynamical simulations that include a self-consistent treatment of star-formation and chemical enrichment of the intergalactic medium, that allows us to follow the evolution of different metal species. We construct a set of simulated light-cones to make predictions of the emission in the 0.3-10 keV energy range. We obtain that GWs increase by a factor of 2 the emission of both galaxy clusters and WHIM. The amount of oxygen at average temperature and, consequently, the amount of expected bright Ovii and Oviii lines is increased by a factor of 3 due to GWs and by 20 per cent when assuming a top-heavy IMF. We compare our results with current observational constraints and find that the emission from faint groups and WHIM should account from half to all of the unresolved X-ray background in the 1-2 keV band.