Origin of cool gas in clusters. Here we show the fraction of tracers that contribute to z = 0 cool gas in clusters, from TNG-Cluster, in each of four origin categories, as a function of redshift. The categories are: “unbound” tracers that are outside of all halos (top left), “other halo” tracers that are within a halo other than the main progenitor of the z = 0 cluster (top right), “primary halo” tracers that are within the central galaxy or diffuse ICM of the main progenitor (bottom left), and “satellite” tracers that are within satellite galaxies (i.e. satellite subhalos) of the main progenitor (bottom right). See Section 2.2. Each halo of TNG-Cluster is shown with an individual line, color showing M_200c at z = 0, while the black solid (dashed) line shows the mean (median) trend. The majority of redshift z = 0 cool gas is contributed to clusters by infalling satellite galaxies and merging of other halos.