Evidence for strong evolution in galaxy environmental quenching efficiency between z = 1.6 and z = 0.9

We analyse the evolution of environmental quenching efficiency, the fraction of quenched cluster galaxies that would be star-forming if they were in the field, as a function of redshift in 14 spectroscopically confirmed galaxy clusters with 0.87 < $z$ < 1.63 from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS). The clusters are the richest in the survey at each redshift. Passive fractions rise from $42_{-13}^{+10}$% at $z$ ∼ 1.6 to $80_{-9}^{+12}$% at $z$ ∼ 1.3 and $88_{-3}^{+4}$% at $z$ < 1.1, outpacing the change in passive fraction in the field. Environmental quenching efficiency rises dramatically from $16_{-19}^{+15}$% at $z$ ∼ 1.6 to $62_{-15}^{+21}$% at $z$ ∼ 1.3 and $73_{-7}^{+8}$% at $z$ ≲ 1.1. This work is the first to show direct observational evidence for a rapid increase in the strength of environmental quenching in galaxy clusters at $z$ ∼ 1.5, where simulations show cluster-mass halos undergo non-linear collapse and virialisation.