2018MNRAS.473L..79B

We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive (<M₂₀₀> = 10¹⁵ M_☉) clusters at 0.15 < z < 0.3. Highly complete spectroscopic coverage combined with 24 µm imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star-forming galaxies down to a stellar mass limit of M_* = 2 x 10¹⁰ M_☉. The fraction f_SF of star-forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At R ≃ 1.3 r₂₀₀, the fraction of star-forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star-formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.