Specific column density ratios may be used as diagnostic probes
of the ionization state, temperature, and metallicity in radiatively
cooling gas. For CIE, the ion fractions are independent of the
metallicity, and the column density ratios depend only on
the gas temperature. However, for non-equilibrium cooling the ion fractions
also depend on Z, and hence so do the column density ratios.
Online Tool:
In the figures generated here (see, for example, figure 9 in
text)
we display "cooling trajectories" for two ionic ratios.
Use the drop-down lists to select the ratios to be displayed along the
x- and y-axes. Use the buttons on the right to select whether results should
be displayed for isochoric or isobaric cooling. Then press "Submit Query".
Results would appear in a couple of minutes.
The gas temperature is represented by color
along the curves, from hot (red) to cool (blue).
Panel (a) shows the behavior
for CIE, for which the results are independent of Z.
Panels (b)-(f) are
for non-equilibrium isochoric cooling, for Z from
10-3 to 2.
The CIE trajectory is reproduced as the grey curves in panels (b)-(f).
