Evidence for a change in the dominant satellite galaxy quenching mechanism at z = 1

We present an analysis of galaxies in groups and clusters at 0.8 < z < 1.2, from the GCLASS and GEEC2 spectroscopic surveys. We compute a ‘conversion fraction’ fconvert that represents the fraction of galaxies that were prematurely quenched by their environment. For massive galaxies, Mstar > 1010.3 M⊙, we find fconvert ∼ 0.4 in the groups and ∼0.6 in the clusters, similar to comparable measurements at z = 0. This means the time between first accretion into a more massive halo and final star formation quenching is tp ∼ 2 Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, …