Average profile of primordial halos at z = 18. The top plot shows the mass-average gas temperature versus the density, the bottom gives f_HD/f_H2 versus the gas density. The color map corresponds to f_HD/f_H2. All halos have similar mass, between 1.4 × 10⁶ M_⊙ and 1.6 × 10⁶ M_⊙. The only difference among theses is f_HD/f_H2, which is indicated via the line color and the color bar on the right. f_HD/f_H2 is computed via a mass-average mean of the gas within the virial radius.