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 which 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. The clusters are the richest in the survey at each redshift. Passive fractions rise from 42_-13 ⁺¹⁰ per cent at z ~ 1.6 to 80_-9 ⁺¹² per cent at z ~ 1.3 and 88_-3 ⁺⁴ per cent at z < 1.1, outpacing the change in passive fraction in the field. Environmental quenching efficiency rises dramatically from 16_-19 ⁺¹⁵ per cent at z ~ 1.6 to 62_-15 ⁺²¹ per cent at z~1.3 and 73_-7 ⁺⁸ per cent 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 haloes undergo non-linear collapse and virialization.