SPL fit of baryon mass fraction f_bar in IllustrisTNG at R_500c and redshift z. Black dots show individual haloes; the green region indicates the SPL fit. Each panel is labelled with their corresponding simulation tag and the value for the α_SPL slope from the SPL fit in the upper-left corner. Top panels: The fraction of baryons includes the hot gas and the galaxy stellar mass within the $2\times R_{M_{\mathrm{star}}/2}\sim r_{\mathrm{op}}$ aperture. Bottom panels: fraction of baryons includes all the gas and all stars inside the halo. The shaded areas are represented with a width of 3σ.