have begun to probe the hydrogen gas from the intergalactic medium (IGM). In particular, cross-correlation of neutral hydrogen (HI) 21 cm intensity maps, together with galaxy surveys at $z\sim0.8$ have given strong evidence for the existence of HI gas in galaxies below the detection limit in the cosmic web [@art:chang10; @art:masui13]. Furthermore, at higher redshift, signs of filamentary structure in the gas have been detected in absorption in the spectra of background sources [e.g., @art:abs1; @art:abs2; @art:abs3; @art:finley14]. Nonetheless, the number of direct detections of the IGM in filaments is still limited to a few in the vicinity of galaxies in the circumgalactic medium and the size of the detected filaments is relatively small at a few $\sim100$ kpc [e.g., @art:film31m33; @art:fildet].\
The IGM can be divided into two main components: the Warm-Hot Intergalactic Medium (WHIM) with temperatures of $\sim10^5-10^7$ K and a cooler component with temperatures up to $\sim10^5$ K  [@art:cen93; @art:evrard94]. The WHIM consists of highly ionized gas that is heated by local galaxies, but predominantly shock-heated during structure formation, and is expected to contain a large fraction of the baryonic matter in the IGM  [e.g., @art:yoshida05]. The existence of significant amounts of hot gas in large-scale filaments 