three different UVB models (after removing the 10$\%$ lowest and highest outliers). The values are given in order of increasing HI photo-ionization rate ($\Gamma_{\rm HI}$) at $z$=0. The error on the signal denotes the standard deviation of the distribution of filament signals. The HI column densities $N_{\rm HI}^{\rm all}$ have been determined from the mean filament signals over a 100 km $\mathrm{s}^{-1}$ velocity width, corresponding to twice the filament radius of  [$0.5\, h^{-1}\, \mathrm{Mpc}$]{} at $z$ = 0.01. $N_{\rm HI}^{10 \%}$ denotes the column density based on the mean filament signal in the brightest 10 per cent of the cells within filaments in the simulation.

\[tab:uvbsigs\]

Due to its high photo-ionization rate, the model also gives the lowest signal limit. However, the photo-ionization rate of this model lies above the limits derived from observations of H$\alpha$ emission in a nearby galaxy [@art:uvbmeasure]. The model on the other hand, results in the highest signal, but its photo-ionization rate lies below the observed limits. The UVB model by is fully consistent with those limits and results in a filament signal that is a factor $\sim$3 lower than the one derived using . The difference between the mean signals from the and is 