Skip to main content


Author(s): Herrera-Camus, Rodrigo; Bolatto, A; Smith, JD; Draine, Bruce T.; Pellegrini, Eric W.; et al

To refer to this page use:
Abstract: The [N II] 122 and 205 pm transitions are powerful tracers of the ionized gas in the interstellar medium. By combining data from 21 galaxies selected from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141 spatially resolved regions with a typical size of similar to 1 kpc, with observations of both [N far-infrared lines. We measure [N II] 122/205 line ratios in the similar to 0.6-6 range, which corresponds to electron gas densities of ne similar to 1-300 cm(-3), with a median value of n(e) = 30 cm(-3). Variations in the electron density within individual galaxies can be as high as a factor of similar to 50, frequently with strong radial gradients. We find that ne increases as a function of infrared color, dust-weighted mean starlight intensity, and star-formation rate (SFR) surface density (Sigma(SFR)). As the intensity of the [N II] transitions is related to the ionizing photon flux, we investigate their reliability as tracers of the SFR. We derive relations between the [N II] emission and SFR in the low-density limit and in the case of a lognormal distribution of densities. The scatter in the correlation between [N II] surface brightness and Sigma(SFR) can be understood as a property of the ne distribution. For regions with ne close to or higher than the [N II] line critical densities, the low-density limit [N n]-based SFR calibration systematically underestimates the SFR because the [N II] emission is collisionally quenched. Finally, we investigate the relation between [N II] emission, SFR, and ne by comparing our observations to predictions from the MAPPINGS-III code.
Publication Date: 1-Aug-2016
Electronic Publication Date: 29-Jul-2016
Citation: Herrera-Camus, R, Bolatto, A, Smith, JD, Draine, B, Pellegrini, E, Wolfire, M, Croxall, K, de Looze, I, Calzetti, D, Kennicutt, R, Crocker, A, Armus, L, van der Werf, P, Sandstrom, K, Galametz, M, Brandl, B, Groves, B, Rigopoulou, D, Walter, F, Leroy, A, Boquien, M, Tabatabaei, FS, Beirao, P. (2016). THE IONIZED GAS IN NEARBY GALAXIES AS TRACED BY THE[N II] 122 AND 205 mu m TRANSITIONS. ASTROPHYSICAL JOURNAL, 826 (10.3847/0004-637X/826/2/175
DOI: doi:10.3847/0004-637X/826/2/175
ISSN: 0004-637X
EISSN: 1538-4357
Type of Material: Journal Article
Journal/Proceeding Title: ASTROPHYSICAL JOURNAL
Version: Final published version. Article is made available in OAR by the publisher's permission or policy.
Notes: Supplementary data may be available at , and

Items in OAR@Princeton are protected by copyright, with all rights reserved, unless otherwise indicated.