Non-equilibrium chemistry and cooling in the diffuse interstellar medium

A. J. Richings, J. Schaye and B. D. Oppenheimer

Dominant coolants in chemical equilibrium

Below we present a series of figures showing the equilibrium ionisation fractions (left panels) and cooling functions (right panels) at various densities in the range 10-2 < nH, tot < 104 and for different metallicities (Zsol, 0.1Zsol and primordial). We compare the results from our model (solid lines) to those predicted by the photoionisation code Cloudy (dashed lines). Each figure shows results in the presence of four different UV radiation fields: the Black (1987) interstellar radiation field multiplied by a factor of 10 (ISRF10; top row), the Black (1987) interstellar radiation field (ISRF; second row), the Haardt & Madau (2001) extragalactic UV background (UVB; third row) and in the absence of UV radiation (None; bottom row). In each row we show show only those species that contribute at least 20 per cent to the cooling rate anywhere in the temperature range 102 K < T < 104 K. The shaded grey region highlights temperatures below 100 K that are outside the range of temperatures that we are primarily interested in, but we include this regime here for completeness. The figure at a density nH, tot = 1 cm-3 and solar metallicity Zsol corresponds to figure 3 of paper I.

nH, tot (cm-3)

We have also tabulated which species dominate the cooling at which temperatures. For every density, metallicity and UV radiation field given above, we determine which species contribute at least 5 per cent to the total cooling rate anywhere in the temperature range 10 2 K < T < 109 K. For each of these we then calculate the minimum and maximum temperatures at which they contribute at least 5 per cent, the temperature at which their contribution is greatest and their peak contribution to the total cooling rate. These tables can be found below.

Last modified: Thu Mar 20 18:15:28 2014