2D histograms of the temperature – density profiles for the halos at the point at which they were extracted from the initial cosmological simulation, weighted by total gas mass within each 2D bin. The halos have begun to gravitationally collapse via atomic cooling as seen from the close to isothermal temperature profile. They differ from the regular H₂ minihalo case by the absence of a sharp drop in temperature to ∼200 K beginning at ∼10⁻²³ g cm⁻³.