The Origins of [C ii] Emission in Local Star-forming Galaxies Journal Articles uri icon

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  • The [CII] 158um fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [CII] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [CII] emission remains unclear, because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [CII] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [NII] 205um fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [CII]/[NII] 122um. Using the FIR [CII] and [NII] emission detected by the KINGFISH and Beyond the Peak Herschel programs, we show that 60-80% of [CII] emission originates from neutral gas. We find that the fraction of [CII] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [CII] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.


  • Croxall, KV
  • Smith, JD
  • Pellegrini, E
  • Groves, B
  • Bolatto, A
  • Herrera-Camus, R
  • Sandstrom, KM
  • Draine, B
  • Wolfire, MG
  • Armus, L
  • Boquien, M
  • Brandl, B
  • Dale, D
  • Galametz, M
  • Hunt, L
  • Kennicutt, R
  • Kreckel, K
  • Rigopoulou, D
  • Werf, P van der
  • Wilson, Christine D

publication date

  • August 20, 2017