Cooling redshift for z = 0 cool gas in clusters. As in Figure 10, we use TNG-Cluster and the tracers that contribute to z = 0 cool gas. Left: Mean distribution of cooling redshifts, defined as when gas associated with the selected tracers cools below the threshold value of 10^4.5 K for the first (orange) or last (blue) time. The solid (dashed) line marks the position of the mean (median) cooling redshift for each of the distributions. Right: mean redshift of final cooling per cluster as a function of halo mass at z = 0. Color denotes the cool gas fraction at redshift z = 0, while the black dashed line shows the median relation. The gas that eventually forms redshift z = 0 cool gas typically cools and heats up multiple times before cooling for the final time around z ∼ 0.1, potentially a signature of pre-processing in other halos.