HI fractions determined for the other UVB models are underestimated. This also results in a lower HI 21 cm signal. The estimates of the filament signal in this work that adopt the and UVB models should thus be considered as lower limits.\

Contamination by galaxies {#sec:galcont}
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One thing to take into account for the observations is that emission from galaxies will contaminate the IGM signal. The voxels in the datacube containing the galaxies can be masked and the SKA has sufficient resolution to do this without losing significant fractions of the volume of a filament. The difficulty lies in finding the positions of the galaxies. Surveys, such as SDSS can provide the positions of the most massive galaxies, but that still leaves contamination by the weaker ones. In , this remaining contamination was estimated to be of the order of $\sim10\%$ after masking SDSS galaxies. Since the IGM signal estimates obtained from the EAGLE simulation used in this work are lower, signifying a lower neutral fraction and thus less HI gass, the contamination due to the faint galaxies not detected by SDSS will also be higher. However, SKA itself will be much more sensitive than SDSS, allowing the localisation 