Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies
- Creators
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Dale, D. A.
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Smith, J. D. T.
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Armus, L.
- Buckalew, B. A.
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Helou, G.
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Kennicutt, R. C., Jr.
- Moustakas, J.
- Roussel, H.
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Sheth, K.
- Bendo, G. J.
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Calzetti, D.
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Draine, B. T.
- Engelbracht, C. W.
- Gordon, K. D.
- Hollenbach, D. J.
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Jarrett, T. H.
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Kewley, L. J.
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Leitherer, C.
- Li, A.
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Malhotra, S.
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Murphy, E. J.
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Walter, F.
Abstract
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.
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.Attached Files
Published - DALapj06.pdf
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Additional details
- Eprint ID
- 18848
- Resolver ID
- CaltechAUTHORS:20100629-095238210
- 1224769
- NASA/JPL/Caltech
- 1407
- NASA
- Created
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2010-06-29Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)