require an accurate measurement of the size of each galaxy. Due to the interferometric nature of the SKA, sources such as galaxies that are brighter than the extended emission from the IGM will also add strong sidelobe noise that needs to be removed from the datacube before extracting the IGM signal. This will be discussed in more detail in Section \[sec:interfero\].\
Fig. \[fig:boxsigdens\] shows the distribution of HI 21 cm differential brightness temperature as a function of the overdensity of the cells in the simulation box, assuming the UVB and after masking the galaxies and their CGM. The baryonic physics included in EAGLE yield a wide distribution of signals for a given density that spans more than 4 orders of magnitude. The small number of bright cells that can be seen above the main distribution corresponds to regions in the CGM of large galaxies that were not masked with the adopted fixed masking radius. Since the number density of these cells is small, their effect on the targeted IGM signal is minimal.

Filament extraction {#sec:simfil}
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Although filaments can be easily identified by eye in slices of the simulation box, fully extracting these three-dimensional structures is difficult. For this study, 