Finding and characterising WHIM structures using the luminosity density
  method
  We have developed a new method to approach the missing baryons problem. We
assume that the missing baryons reside in a form of Warm Hot Intergalactic
Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large
scale structure in the spatial distribution of galaxies that traces the Cosmic
Web and that in hydrodynamical simulations is associated to the WHIM, (b) map
its luminosity into a galaxy luminosity density field, (c) use numerical
simulations to relate the luminosity density to the density of the WHIM, (d)
apply this relation to real data to trace the WHIM using the observed galaxy
luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our
application we find evidence for the WHIM along the line of sight to the
Sculptor Wall, at redshifts consistent with the recently reported X-ray
absorption line detections. Our indirect WHIM detection technique complements
the standard method based on the detection of characteristic X-ray absorption
lines, showing that the galaxy luminosity density is a reliable signpost for
the WHIM. For this reason, our method could be applied to current galaxy
surveys to optimise the observational strategies for detecting and studying the
WHIM and its properties. Our estimates of the WHIM hydrogen column density in
Sculptor agree with those obtained via the X-ray analysis. Due to the
additional column density estimate, our method has potential for improving the
constrains of the physical parameters of the WHIM as derived with X-ray
absorption, and thus for improving the understanding of the missing baryons
problem.
