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Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies

Dale, D. A. and Smith, J. D. T. and Armus, L. and Buckalew, B. A. and Helou, G. and Kennicutt, R. C., Jr. and Moustakas, J. and Roussel, H. and Sheth, K. and Bendo, G. J. and Calzetti, D. and Draine, B. T. and Engelbracht, C. W. and Gordon, K. D. and Hollenbach, D. J. and Jarrett, T. H. and Kewley, L. J. and Leitherer, C. and Li, A. and Malhotra, S. and Murphy, E. J. and Walter, F. (2006) Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies. Astrophysical Journal, 646 (1). pp. 161-173. ISSN 0004-637X. doi:10.1086/504835.

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Mid-infrared diagnostics are presented for a large portion of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archival data from ISO and Spitzer. The SINGS data set includes low- and high-resolution spectral maps and broadband imaging in the infrared for over 160 nuclear and extranuclear regions within 75 nearby galaxies spanning a wide range of morphologies, metallicities, luminosities, and star formation rates. Our main result is that these mid-infrared diagnostics effectively constrain a target's dominant power source. The combination of a high-ionization line index and PAH strength serves as an efficient discriminant between AGNs and star-forming nuclei, confirming progress made with ISO spectroscopy on starbursting and ultraluminous infrared galaxies. The sensitivity of Spitzer allows us to probe fainter nuclear and star-forming regions within galaxy disks. We find that both star-forming nuclei and extranuclear regions stand apart from nuclei that are powered by Seyfert or LINER activity. In fact, we identify areas within four diagnostic diagrams containing >90% Seyfert/LINER nuclei or >90% H II regions/H II nuclei. We also find that, compared to starbursting nuclei, extranuclear regions typically separate even further from AGNs, especially for low-metallicity extranuclear environments. In addition, instead of the traditional mid-infrared approach to differentiating between AGNs and star-forming sources that utilizes relatively weak high-ionization lines, we show that strong low-ionization cooling lines of X-ray-dominated regions like [Si II] 34.82 μm can alternatively be used as excellent discriminants. Finally, the typical target in this sample shows relatively modest interstellar electron density (~400 cm^(-3)) and obscuration (A_V ~ 1.0 mag for a foreground screen), consistent with a lack of dense clumps of highly obscured gas and dust residing in the emitting regions.

Item Type:Article
Related URLs:
URLURL TypeDescription
Dale, D. A.0000-0002-5782-9093
Smith, J. D. T.0000-0003-1545-5078
Armus, L.0000-0003-3498-2973
Helou, G.0000-0003-3367-3415
Kennicutt, R. C., Jr.0000-0001-5448-1821
Sheth, K.0000-0002-5496-4118
Calzetti, D.0000-0002-5189-8004
Draine, B. T.0000-0002-0846-936X
Jarrett, T. H.0000-0002-4939-734X
Kewley, L. J.0000-0001-8152-3943
Leitherer, C.0000-0003-2685-4488
Malhotra, S.0000-0002-9226-5350
Murphy, E. J.0000-0001-7089-7325
Walter, F.0000-0003-4793-7880
Additional Information:© 2006 American Astronomical Society. Received 2006 February 24; accepted 2006 March 31. Mike Brotherton provided helpful comments. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through contract 1224769 issued by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. This research has made use of the NASA/IPAC Extragalactic Database, which is operated by JPL/Caltech, under contract with NASA. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:active; galaxies: nuclei; H ii regions; infrared: galaxies; infrared: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20100629-095238210
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Official Citation:D. A. Dale et al 2006 ApJ 646 161 doi: 10.1086/504835
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18848
Deposited On:29 Jun 2010 20:13
Last Modified:08 Nov 2021 23:47

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