Studying the Warm-Hot Intergalactic Medium in Emission
  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.
