approaching the values of the field galaxy sample only at $\sim 5r_{200}$ (corresponding to 10Mpc for a massive cluster). Moreover, the SF in low-mass cluster galaxies (M=10$^{9-9.5}$M$_{\odot}$) still shows a significant discrepancy even at this large radius with respect to that of the field galaxies. According to the authors, three main causes can explain the observed trends: i) ‘pre-processing’ of galaxies within infalling groups; ii) ‘overshooting’ for those galaxies that are not falling in for the first time (also called ‘backsplash’ galaxies); iii) ram-pressure stripping. Of course, the three mechanisms act differently depending on the galaxy and host halo mass and the clustercentric distance, but in any case the radial trend of the hot gas cannot be explained solely by overshooting and pre-processing. A direct interaction with the host group/cluster is also required and their simulations suggest that ram-pressure stripping can strip the hot gas from low- and high-mass galaxies out to several times $r_{200}$, although it cannot affect the cold gas except for the low-mass galaxies. The authors also claimed that tidal interaction does not play an important role in the gas removal, but it should be an important factor in the morphological transformation of these galaxies.

S0s differ 