The Ionized Gas in Nearby Galaxies as Traced by the [NII] 122 and 205 um Transitions
Rodrigo Herrera-Camus (Max Planck Institute for Extraterrestrial Physics Garching, University of Maryland)
Alberto Bolatto (University of Maryland)
J. D T Smith (University of Toledo)
Bruce Draine (Princeton University)
E. Pellegrini (Universität Heidelberg)
Mark Wolfire (University of Maryland)
Kevin Croxall (The Ohio State University)
Ilse De Looze (University of Cambridge)
D. Calzetti (University of Massachusetts Amherst)
Robert Kennicutt (Universität Heidelberg)
A. Crocker (Reed College)
Lee Armus (California Institute of Technology)
P. Van Der Werf (Universiteit Leiden)
Karin Sandstrom (University of California)
Maud Galametz (European Southern Observatory)
Bernhard Brandl (Universiteit Leiden, TU Delft - Aerospace Engineering)
Brent Groves (Australian National University)
D. Rigopoulou (University of Oxford)
Fabian Walter (Max-Planck-Institut für Astronomie)
A. Leroy (The Ohio State University)
Mederic Boquien (University of Cambridge)
F. S. Tabatabaei (Instituto de Astrofísica de Canarias)
Pedro Beirão (Observatoire de Paris)
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Abstract
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).