  Hydrodynamic simulations predict that a significant fraction of the gas in
the current Universe is in the form of high temperature, highly ionized plasma
emitting and absorbing primarily in the soft X-ray and UV bands, dubbed the
Warm-Hot Intergalactic Medium (WHIM). Its signature should be observable in
red-shifted emission and absorption lines from highly ionized elements. To
determine the expected WHIM emission in the soft X-ray band we used the output
of a large scale hydrodynamic SPH simulation to generate images and spectra
with angular resolution of 14'' and energy resolution of 1 eV. The current
biggest limit of any hydrodynamic simulation in predicting the X-ray emission
comes from metal diffusion. In our investigation, by using four different
models for the WHIM metallicity we have found a strong dependence of the
emission on the model used, with differences up to almost an order of
magnitude. For each model we have investigated the redshift distribution and
angular scale of the emission, confirming that most photons come from redshift
z<1.2 and that the emission has a typical angular scale of less than a few
arcminutes. We also compared our simulations with the few currently available
observations and found that, within the variation of the metallicity models,
our predictions are in good agreement with current constraints on the WHIM
emission, and at this time the weak experimental constraints on the WHIM
emission are not sufficient to exclude any of the models used.
