CaltechAUTHORS
Published August 1, 2016 | Version Published + Submitted
Journal Article Open

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

Creators

  • 1. ROR icon University of Maryland, College Park
  • 2. ROR icon Max Planck Institute for Extraterrestrial Physics
  • 3. ROR icon University of Toledo
  • 4. ROR icon Princeton University
  • 5. ROR icon Heidelberg University
  • 6. ROR icon The Ohio State University
  • 7. ROR icon University of Cambridge
  • 8. ROR icon University of Massachusetts Amherst
  • 9. ROR icon Reed College
  • 10. ROR icon California Institute of Technology
  • 11. ROR icon Leiden University
  • 12. ROR icon University of California, San Diego
  • 13. ROR icon European Southern Observatory
  • 14. ROR icon Delft University of Technology
  • 15. ROR icon Australian National University
  • 16. ROR icon University of Oxford
  • 17. ROR icon Max Planck Institute for Astronomy
  • 18. ROR icon Instituto de Astrofísica de Canarias
  • 19. ROR icon Paris Observatory

Abstract

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.

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.

Attached Files

Published - apj_826_2_175.pdf

Submitted - 1605.03180v1.pdf

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Additional details

Identifiers

Eprint ID
69306
Resolver ID
CaltechAUTHORS:20160729-110126806

Related works

Describes
https://arxiv.org/abs/1605.03180 (URL)

Funding

Fulbright Foundation
NSF
AST-0955836
NASA/JPL
1373858
NSF
AST-1412419
Research Corporation
NASA/JPL
RSA 1427378
Alexander von Humboldt Foundation
Max Planck Institute für Astronomie
Ministerio de Economía y Competitividad (MINECO)
AYA2013-41243-P
NASA/JPL/Caltech
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)

Dates

Created
2016-07-29
Created from EPrint's datestamp field
Updated
2021-11-11
Created from EPrint's last_modified field

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Physics Department