Croxall, K. V.K. V.CroxallSmith, J. D.J. D.SmithPellegrini, E.E.PellegriniGroves, B.B.GrovesBolatto, A.A.BolattoHerrera-Camus, R.R.Herrera-CamusSandstrom, K. M.K. M.SandstromDraine, B.B.DraineWolfire, M. G.M. G.WolfireArmus, L.L.ArmusBoquien, M.M.BoquienBrandl, B.B.BrandlDale, D.D.DaleGalametz, M.M.GalametzHUNT, Leslie KippLeslie KippHUNTKennicutt, R., Jr.R., Jr.KennicuttKreckel, K.K.KreckelRigopoulou, D.D.Rigopoulouvan der Werf, P.P.van der WerfWilson, C.C.Wilson2020-08-202020-08-2020170004-637Xhttp://hdl.handle.net/20.500.12386/26744The [C II] 158 μm fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [C II] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [C II] emission remains unclear because C<SUP>+</SUP> can be found in multiple phases of the interstellar medium. Here we measure the fractions of [C II] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [N II] 205 μm fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [C II]/[N II] 122 μm. Using the FIR [C II] and [N II] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%─80% of [C II] emission originates from neutral gas. We find that the fraction of [C II] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [C II] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.STAMPAenArticle10.3847/1538-4357/aa80352-s2.0-85028757333000407801100006https://iopscience.iop.org/article/10.3847/1538-4357/aa80352017ApJ...845...96CFIS/05 - ASTRONOMIA E ASTROFISICAPE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation