The Origins of [C II] Emission in Local Star-forming Galaxies

Journal article (2017)

Authors

K. V. Croxall Ohio State University, Illumination Works LLC, Max-Planck-Institut für Astronomie
J. D T Smith Max-Planck-Institut für Astronomie, University of Toledo
Mederic Boquien Universidad de Antofagasta
B.R. Brandl Universiteit Leiden,
Daniel A. Dale University of Wyoming
Maud Galametz European Southern Observatory, ENS-PSL Research University & CNRS
L. K. Hunt INAF-Osservatorio Astrofisico di Arcetri
R. C. Kennicutt University of Cambridge
K. Kreckel Max-Planck-Institut für Astronomie
D. Rigopoulou University of Oxford
P. Van Der Werf Universiteit Leiden
C Wilson McMaster University
E. Pellegrini University of Toledo, University of Heidelberg
Brent Groves Australian National University
Alberto Bolatto University of Maryland
Rodrigo Herrera-Camus Max Planck Institute for Extraterrestrial Physics Garching
Karin Sandstrom University of California
Bruce Draine Princeton University
Mark Wolfire University of Maryland
Lee Armus Spitzer Science Center
Copyright: © 2017 K. V. Croxall, J. D T Smith, E. Pellegrini, Brent Groves, Alberto Bolatto, Rodrigo Herrera-Camus, K. M. Sandstrom, Bruce Draine, M. G. Wolfire, Lee Armus, Mederic Boquien, B.R. Brandl, Daniel A. Dale, Maud Galametz, L. K. Hunt, R. C. Kennicutt, K. Kreckel, D. Rigopoulou, p van der werf, C Wilson
DOI: https://doi.org/10.3847/1538-4357/aa8035
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Published Date

20-08-2017

Language

English

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Abstract

The [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+ 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.

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