Predictions for the gas distribution within a cluster of galaxies derived from the Illustris simulations (http://www.illustris-project.org/explorer; Nelson et al. 2015). Tails of stripped gas that are ~50 kpc long (upper right panel) are expected to be associated with most of the simulated cluster galaxies. Once stripped from galaxies and injected into the hot (10⁷ –10⁸ K) ICM, the gas is ionised by heat conduction, turbulence, MHD waves and extraplanar star formation in the tails. It then becomes visible in deep, wide-field NB Hα imaging. Some gas associated to star forming regions within the galactic disc can also be stripped in its ionised phase. Tails of ionised gas similar to those predicted by the simulations are indeed observed in the Hα continuum-subtracted image of the two galaxies CGCG 97-73 and 97-79 in A1367 obtained with Suprime-Cam at the Subaru telescope (10′× 10′) (Boselli & Gavazzi 2014; Yagi et al. 2017). Similar tails of ionised gas will be detected by VESTIGE.