Total [C ii] luminosity of a hypothetical AGN versus galactic radius for a range of X-ray luminosities. The key labels the log of the X-ray luminosity and ranges from LogL(X-ray) = 40 to 48. The decrease in [C ii] luminosity with increasing L(X-ray) is due to the destruction of C⁺ in the WIM close to the source of X-rays. The radius over which the X-rays photoionize C⁺ increases with increasing X-ray luminosity.