[HM12 hereupon] results in the lowest photo-ionization rate. These models adopt the same methodology, but the uses an updated description of the ionizing sources to adress the observational constraints available at the time. This includes X-ray emission from AGN and UV emission from starforming galaxies at all redshifts, as well as a more detailed treatment of absorption. The most recent continuation of this set of models is given by @art:hm18 [henceforth P18] with an intermediate photo-ionization rate and includes new constraints on the column density distribution of HI absorbers and a new treatment of the opacity for ionizing photons in the IGM. Each of these backgrounds will result in a different filament signal strength and this uncertainty in the intensity of the UVB and its implications will be discussed in more detail in Section \[sec:uvb\]. We note that the EAGLE simulation itself adopts the UVB model. Adopting a different UVB photoionization rate for determining the HI fraction is not fully self-consistent, since the IGM temperature was computed assuming the model. Given that the two other UVB models that we consider have lower photoionization and heating rates, we can infer that by using the temperature provided by the EAGLE simulation, the 