The Ionized Gas in Nearby Galaxies as Traced by the [NII] 122 and 205 um Transitions

Rodrigo Herrera-Camus, Alberto Bolatto, J. D T Smith, Bruce Draine, E. Pellegrini, Mark Wolfire, Kevin Croxall, Ilse De Looze, D. Calzetti, Robert Kennicutt, A. Crocker, Lee Armus, P. Van Der Werf, Karin Sandstrom, Maud Galametz, Bernhard Brandl, Brent Groves, D. Rigopoulou, Fabian Walter, A. LeroyMederic Boquien, F. S. Tabatabaei, Pedro Beirão

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The [NII] 122 and 205 um transitions are powerful tracers of the ionized gas in the ISM: (1) the [NII] 122/205 line ratio can be used to measure the electron density of the low-excitation, ionized gas, and (2) the intensity of these lines is directly related to the flux of ionizing photons, probing the most recent star formation activity. The study of these applications in nearby galaxies is specially relevant now that ALMA can observe both [NII] transitions at z>2. In this talk I will present Herschel observations of these pair of [NII] far-infrared lines in 21 nearby galaxies selected from the KINGFISH and Beyond the Peak samples. I will discuss the reliability of the [NII] lines as star formation tracers, and how the electron density of the ionized gas is related to other relevant ISM properties (e.g., radiation field strength, star formation activity, dust temperature, etc).
Original languageEnglish
Number of pages17
JournalThe Astrophysical Journal: an international review of astronomy and astronomical physics
Issue number175
Publication statusPublished - 2016


  • star formation
  • ISM
  • structure


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