located within galaxies, we find that for the IGM in large-scale filaments considered in this work, both removing the starforming particles or fixing their neutral neutral fraction to unity yields the same result.\
The HI 21 cm signal can then further be determined following the prescription outlined in , where we now use the case A hydrogen recombination rate and the corresponding fraction of Lyman $\alpha$ photons per recombination. Case A, where recombinations directly into the ground state are included, is more applicable to the gas considered here than case B, the latter of which was adopted in , since the IGM is optically thin [@book:draine11]. We then use the $YT$ package [@art:yt] to deposit the particles onto a regular grid with $1024^3$ cells, corresponding to a resolution of 66 $h^{-1}$kpc. We adopt a cubic SPH kernel and 58 nearest neighbors, similar to the kernel that was used in EAGLE itself [@art:eagle]. Further analysis in this paper is performed on this gridded box.\
The photo-ionization rate is one of the main uncertainties in this estimation. Here, we consider three different models for the UVB: The @art:hm01 [HM01 after this] UVB gives the highest photo-ionization rate at $z$=0, whereas the @art:hm12 