of X-ray AGN in rich clusters revealing them to be an infalling population with high relative velocities [@HPS12]. This confirms that the transformation of galaxies often occurs (or begins at least) well outside the cluster cores, in groups or as infalling galaxies enter the virialized region for the first time [@MET05].

Hints about the distribution of galaxy luminosity, colours and morphology in the filaments have been given by @PB06, who found that brighter galaxies have a less filamentary distribution than the fainter ones. With respect to the morphology, the early-type galaxies are concentrated in the vicinity of the nodes, while spiral galaxies are sparsely distributed across the filaments. @FBM08 observed that the fraction of starburst galaxies in the filaments around the cluster A1763 is twice that in other cluster regions as detected by [*Spitzer*]{} and suggested that filaments are a sort of [*galaxy reservoir*]{} for clusters.

By studying a sample of supercluster filaments in the two-degree Field Galaxy Redshift Survey, @PRP08 observed a sudden enhancement in SF in faint dwarf galaxies outside the cluster virial radius. They interpreted their findings with a close interaction and/or harassment with other infalling galaxies along the same filaments. Another possible explanation is the very 