Scatter plot of temperature for baryonic gas as a function of dark matter density. Panels (a)–(f) are for z = 4–0, respectively. Gas with T < 10⁵ K is the warm gas, gas with T > 10⁷ K is the hot gas, and gas with temperatures between these two ranges is the WHIM. Note that regions of temperature below 10⁴ K in the TNG data are not well resolved, particularly for the cells of star-forming gas (see Springel & Hernquist 2003), and should be interpreted with caution.