Satellite quenching was not important for z ∼ 1 clusters: most quenching occurred during infall

We quantify the relative importance of environmental quenching versus pre-processing in z ~ 1 clusters by analysing the infalling galaxy population in the outskirts of 15 galaxy clusters at 0.8 < z < 1.4 drawn from the GOGREEN and GCLASS surveys. We find significant differences between the infalling galaxies and a control sample; in particular, an excess of massive quiescent galaxies in the infalling region. These massive infalling galaxies likely reside in larger dark matter haloes than similar-mass control galaxies because they have twice as many satellite galaxies. Furthermore, these satellite galaxies are distributed in an NFW profile with a larger scale radius compared to the satellites of the control galaxies. Based on these findings, we conclude that it may not be appropriate to use 'field' galaxies as a substitute for infalling pre-cluster galaxies when calculating the efficiency and mass dependence of environmental quenching in high-redshift clusters. By comparing the quiescent fraction of infalling galaxies at 1 < R/R₂₀₀<3 to the cluster sample (R/R₂₀₀<1) we find that almost all quiescent galaxies with masses >10¹¹ M_⊙ were quenched prior to infall, while up to half of lower mass galaxies were environmentally quenched after passing the virial radius. This means most of the massive quiescent galaxies in z ~ 1 clusters were self-quenched or pre-processed prior to infall.