Abundance of HI as a function of gas temperature in the ISM of our MBH4_full simulation (at t ∼ 380 Myr), mass-weighted by the total amount of H per bin. The ISM is split into different phases based on its HI, HII or H₂ abundance, and gas temperature, following the definitions of Kim et al. (2023b) (summarised in Table 3). The CMM and WIM are categorised by their H₂ and HII abundance, respectively. For the CMM, χ_H2 > 0.25, meaning that χ_HI < 0.75, while for the WIM, χ_HII > 0.5, implying that χ_HI < 0.5. These upper limits are indicated by blue and green upside-down triangles for the CMM and WIM, respectively.