The [C ii] luminosity of the Milky Way as a function of Galactocentric radius. The estimated contributions to the [C ii] luminosity from gas associated with dense PDRs, ionized gas, CNM H i gas, and CO-dark H₂ gas are also shown. Typical uncertainties are 5% for the total [C ii] luminosity and the contribution from H i gas, 10% for the contribution from CO-dark H₂ gas, and we assume 30% for the contribution from ionized gas. The black dots (and error bars) represent the radial distribution of the SFR derived in Sect. 2.