Fractional mass of cool gas in clusters by origin. Top panel: Mean mass of tracers per cluster in each parent category for all TNG-Cluster clusters at time of crossing 2R_200c (hatched), at crossing R_200c (dotted), and at redshift z = 0 (solid). The parent categories are those defined in Section 2.2 and already characterized in Figures 13 and 14. The rightmost blue bars additionally show the total mass of tracers that never crossed the respective distance, either because they remained outside this distance for all redshifts between z = 8 and today, or because they have constantly been within this radius since z = 8. For the redshift zero category, no such tracer exists, since all tracers are by definition in one of the four parent categories. Since all tracers have the same mass of 1.2 × 10⁷ M_⊙, the relative height of the bars gives the relative number of tracers as well. Bottom panel: Tracer mass in each origin category for individual clusters versus M_200c of the respective cluster at z = 0. The colors and respective categories are identical to the top panel. Each cluster is associated with five markers, one for each category. The majority of redshift z = 0 cool gas predecessors is carried into the cluster 2R_200c region by satellites and other halos, in which it predominantly also remains until today, while ∼80% of this gas never crosses the virial radius.