Temperature vs density for the three ISM phases in the RECAL-L0025N0752 galaxies. Each phase is represented with a normalised relative frequency between 0.1% and 100%. We observe that each phase is located in a specific region of the temperature vs density plane. The DIG (blue) is characterised by high temperatures (log T[K]≳3.5) and low densities (log n(H)[cm⁻³]≲ − 1), atomic gas (orange) by intermediate densities (−1 ≲ log n(H)[cm⁻³]≲3) with a bridge between high temperatures (log T[K]≈3.5) and low temperatures (log T[K]≈1.4) and molecular gas (green) by high densities (log n(H)[cm⁻³]≳3) and a range of very low temperatures (log T[K]≈1.1) to intermediate temperatures (log T[K]≈2.5) due to H₂ heating processes (Bialy & Sternberg 2019). The temperature-density relation of the original SPH gas particles (inset plot) is shown in purple to demonstrate the need to use a more detailed ISM model when predicting FIR line strengths from these simulations.