Ex situ and in situ origin of the hot inner stellar halo of TNG50 galaxies. Top: probability density distribution of stars on hot orbits, for in situ (left) and ex situ (right) stars separately. Here we divide the subsample of TNG50 galaxies in g6 into five bins according to their ex situ fraction, f_ExSitu. Each curve represents the average p_hot (in situ or ex situ) of galaxies in each bin, color coded by its range of stellar ex situ fraction from 0−0.2 to 0.5−0.7, as indicated by the colored numbers. The curves are normalized such that the total probability of all stars within 2 R_e equals unity. Bottom: stellar ex situ fraction of the galaxy, f_ExSitu, versus the ex situ fraction of stars in the hot inner stellar halo, f_{ExSitu, halo} (3.5 kpc < r < 2 R_e and λ_z < 0.5). Each dot represents one galaxy in TNG50, color coded by galaxies stellar mass, M_*, and crosses denote galaxies in subsample g6 (i.e., with a galaxy stellar mass in the range 10¹¹ − 10^11.6 and an average stellar size).