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The Ionized Gas in Nearby Galaxies as Traced by the [N II] 122 and 205 μm Transitions

Herrera-Camus, R. and Bolatto, A. and Smith, J. D. and Draine, B. and Pellegrini, E. and Wolfire, M. and Croxall, K. and De Looze, I. and Calzetti, D. and Kennicutt, R. and Crocker, A. and Armus, L. and van der Werf, P. and Sandstrom, K. M. and Galametz, M. and Brandl, B. and Groves, B. and Rigopoulou, D. and Walter, F. and Leroy, A. and Boquien, M. and Tabatabaei, F. S. and Beirao, P. (2016) The Ionized Gas in Nearby Galaxies as Traced by the [N II] 122 and 205 μm Transitions. Astrophysical Journal, 826 (2). Art. No. 175. ISSN 0004-637X.

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The [N ii] 122 and 205 μm 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 ~1 kpc, with observations of both [N ii] far-infrared lines. We measure [N ii] 122/205 line ratios in the ~0.6–6 range, which corresponds to electron gas densities of n_e ~ 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 ~50, frequently with strong radial gradients. We find that n_e increases as a function of infrared color, dust-weighted mean starlight intensity, and star-formation rate (SFR) surface density (Σ_(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 log-normal distribution of densities. The scatter in the correlation between [N ii] surface brightness and Σ_(SFR) can be understood as a property of the n_e distribution. For regions with n_e close to or higher than the [N ii] line critical densities, the low-density limit [N ii]-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 n_e by comparing our observations to predictions from the MAPPINGS-III code.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Herrera-Camus, R.0000-0002-2775-0595
Bolatto, A.0000-0002-5480-5686
Smith, J. D.0000-0003-1545-5078
Draine, B.0000-0002-0846-936X
Wolfire, M.0000-0003-0030-9510
Croxall, K.0000-0002-5258-7224
Calzetti, D.0000-0002-5189-8004
Crocker, A.0000-0001-8513-4945
van der Werf, P.0000-0001-5434-5942
Sandstrom, K. M.0000-0002-4378-8534
Galametz, M.0000-0002-0283-8689
Groves, B.0000-0002-9768-0246
Walter, F.0000-0003-4793-7880
Leroy, A.0000-0002-2545-1700
Additional Information:© 2016 The American Astronomical Society. Received 2015 October 29; revised 2016 May 10; accepted 2016 May 10; published 2016 July 29. We thank the anonymous referee for helpful suggestions that improved the paper. RHC acknowledges support from a Fulbright-CONICYT grant. ADB acknowledges partial support from a CAREER grant NSF-AST0955836, from NASA-JPL 1373858, NSF-AST 1412419, and from a Research Corporation for Science Advancement Cottrell Scholar award. Beyond the Peak research has been supported by a NASA/JPL grant (RSA 1427378). JDS gratefully acknowledges visiting support from the Alexander von Humboldt Foundation and the Max Planck Institute für Astronomie. FST acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2013-41243-P. PACS has been developed by a consortium of institutes led by MPE (Germany) and including UVIE (Austria); KU Leuven, CSL, IMEC (Belgium); CEA, LAM (France); MPIA (Germany); INAF-IFSI/OAA/OAP/OAT, LENS, SISSA (Italy); IAC (Spain). This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy), and CICYT/MCYT (Spain). HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS, and SPIRE consortia. SPIRE has been developed by a consortium of institutes led by Cardiff University (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA). This work is based (in part) on observations made with Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Funding AgencyGrant Number
Fulbright FoundationUNSPECIFIED
Research CorporationUNSPECIFIED
Alexander von Humboldt FoundationUNSPECIFIED
Max Planck Institute für AstronomieUNSPECIFIED
Ministerio de Economía y Competitividad (MINECO)AYA2013-41243-P
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)UNSPECIFIED
Subject Keywords:galaxies: ISM – galaxies: star formation – ISM: structure
Issue or Number:2
Record Number:CaltechAUTHORS:20160729-110126806
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69306
Deposited By: Tony Diaz
Deposited On:29 Jul 2016 18:21
Last Modified:03 Oct 2019 10:20

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