Studying the Warm-Hot Intergalactic Medium in Emission

TL;DR

This study evaluates the feasibility of detecting the warm-hot intergalactic medium (WHIM) in emission using future X-ray missions with microcalorimeter detectors, through analysis of simulated spectra to identify emission lines and estimate physical conditions.

Contribution

It demonstrates that upcoming X-ray missions can detect and characterize the WHIM in emission, providing insights into cosmic chemical enrichment and feedback processes.

Findings

Approximately 400 emission features per deg^2 detectable with 1 Ms exposure and 2.5 eV resolution.

Temperature of the WHIM can be estimated with ~20% precision from line ratios.

Detection rate remains significant (~160 per deg^2) even with degraded energy resolution of 7 eV.

Abstract

We assess the possibility to detect the warm-hot intergalactic medium (WHIM) in emission and to characterize its physical conditions and spatial distribution through spatially resolved X-ray spectroscopy, in the framework of the recently proposed DIOS, EDGE, Xenia, and ORIGIN missions, all of which are equipped with microcalorimeter-based detectors. For this purpose we analyze a large set of mock emission spectra, extracted from a cosmological hydrodynamical simulation. These mock X-ray spectra are searched for emission features showing both the OVII K alpha triplet and OVIII Ly alpha line, which constitute a typical signature of the warm hot gas. Our analysis shows that 1 Ms long exposures and energy resolution of 2.5 eV will allow us to detect about 400 such features per deg^2 with a significance >5 sigma and reveals that these emission systems are typically associated with density ~100 above the mean. The temperature can be estimated from the line ratio with a precision of ~20%. The combined effect of contamination from other lines, variation in the level of the continuum, and degradation of the energy resolution reduces these estimates. Yet, with an energy resolution of 7 eV and all these effects taken into account, one still expects about 160 detections per deg^2. These line systems are sufficient to trace the spatial distribution of the line-emitting gas, which constitute an additional information, independent from line statistics, to constrain the poorly known cosmic chemical enrichment history and the stellar feedback processes.