Mapping the IGM in the Cosmic Web in emission and absorption with LEM

The intergalactic medium (IGM) that fills the Cosmic Web filaments is the ultimate repository of everything expelled from galaxies over their lifetime. Its metal content thus encodes the history of the feedback processes in the Universe. The Line Emission Mapper (LEM) will have the requisite spectral resolution and grasp to detect and map the emission in O and Fe lines from the denser ridges of these filaments, outside the halos of clusters and galaxies. We will select the candidate filaments based on galaxy redshift surveys and search for those emission lines at a known redshift, chosen to better see the extremely faint IGM signal through the forest of the Milky Way foreground lines. At the same time, LEM will be able to detect the same IGM filaments in absorption in the cumulative spectrum of the CXB point sources, taking advantage of the large grasp and good angular resolution of the telescope. This will let us constrain the physical parameters of the IGM and the cosmological history of galactic feedback.