[C ii] luminosities of the individual ISM components are plotted as a function of radius in a galactic nucleus with a central X-ray source with L(X-ray) = 10⁴² (top panel) and 10⁴⁴ erg s^-1 (bottom panel) with a filling factor η(PDR) = 2 × 10^-3. The assumed ISM parameters and dimensions of the nucleus are given in the text. The dense WIM dominates the [C ii] emission at L(X-ray) =10⁴⁰ erg s^-1 but is increasingly suppressed with increasing L(X-ray) until the PDRs dominate the emission.