Predicted [C ii]/FIR luminosity ratio versus X-ray luminosity for different PDR filling factors (see Fig. 6). Also plotted are data points for six AGNs (red bullets) observed in [C ii], FIR, and X-rays (Stacey et al. 2010) and two high-redshift AGNs (black squares) observed in [C ii] (as compiled in Gullberg et al. 2015), FIR by Vignali et al. (2005), and X-rays by Law et al. (2004). We assumed 30% uncertainties for the [C ii]/FIR ratios from Stacey et al. (2010) and for the X-ray luminosities.