Non-equilibrium cooling functions

In the figures below we show the non-equilibrium cooling functions of gas that is cooling either isochorically or isobarically. The gas starts in chemical equilibrium at either 10⁴ K or 10⁶ K, then we use our model to follow its chemical evolution as it cools at constant density (isochoric) or at constant pressure (isobaric), recording the cooling rate as a function of temperature. We consider both solar and ten per cent solar metallicities, in the presence of the Black (1987) interstellar radiation field (ISRF) and the Haardt & Madau (2001) extragalactic UV background (UVB). We show results for two densities, n_{H, tot} = 1 cm^-3 and 100 cm^-3. For the isobaric runs, this density is measured at 10⁴ K.

In addition to the cooling functions (top left panel of each figure), we also show the abundances of H₂ (top right panel), CII (bottom left panel) and electrons (bottom right). We compare the isochoric (blue curves) and isobaric(red curves) runs in non-equilibrium (light shades) with their corresponding cooling functions and abundances in chemical equilibrium (dark shades), as indicated in the legend. The figures at solar metallicity in the presence of the Haardt & Madau (2001) UVB correspond to figures 7 and 9 of paper I.

Solar metallicity

Ten per cent solar metallicity

Below we plot the ratio of the cooling rates in non-equilibrium, Λ_NE, and in equilibrium, Λ_Eq, as a function of density and temperature. These are shown for gas cooling isochorically from chemical equilibrium at 10⁴ K or 10⁶ K at a metallicity Z_sol or 0.1 Z_sol, in the presence of the Haardt & Madau (2001) extragalactic UV background. The colour bar indicates the log of the ratio Λ_NE/Λ_Eq. Blue regions indicate where non-equilibrium effects suppress the cooling rate and red regions indicate where the non-equilibrium cooling rate is enhanced with respect to the equilibrium cooling rate. The black region shows where the equilibrium cooling rate is negative, i.e. there is net heating. The minimum temperature to which the cooling gas can cool before there is net heating in non-equilibrium is shown by the white curve.

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Last modified: Thu Mar 20 18:20:35 2014