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Published March 10, 2009 | Published
Journal Article Open

The Spitzer Infrared Nearby Galaxies Survey: A High-Resolution Spectroscopy Anthology

Abstract

High-resolution mid-infrared spectra are presented for 155 nuclear and extranuclear regions from the Spitzer Infrared Nearby Galaxies Survey (SINGS). The fluxes for nine atomic forbidden and three molecular hydrogen mid-infrared emission lines are also provided, along with upper limits in key lines for infrared-faint targets. The SINGS sample shows a wide range in the ratio of [S III] 18.71 μm/[S III] 33.48 μm, but the average ratio of the ensemble indicates a typical interstellar electron density of 300-400 cm^(–3) on ~23" × 15" scales and 500-600 cm^(–3) using ~11" × 9" apertures, independent of whether the region probed is a star-forming nuclear, a star-forming extranuclear, or an active galactic nuclei (AGN) environment. Evidence is provided that variations in gas-phase metallicity play an important role in driving variations in radiation field hardness, as indicated by [Ne III] 15.56 μm/[Ne II] 12.81 μm, for regions powered by star formation. Conversely, the radiation hardness for galaxy nuclei powered by accretion around a massive black hole is independent of metal abundance. Furthermore, for metal-rich environments AGN are distinguishable from star-forming regions by significantly larger [Ne III] 15.56 μm/[Ne II] 12.81 μm ratios. Finally, [Fe II] 25.99 μm/[Ne II] 12.81 μm versus [Si II] 34.82 μm/[S III] 33.48 μm also provides an empirical method for discerning AGN from normal star-forming sources. However, similar to [Ne III] 15.56 μm/[Ne II] 12.81 μm, these mid-infrared line ratios lose their AGN/star-formation diagnostic powers for very low metallicity star-forming systems with hard radiation fields.

Additional Information

© 2009. The American Astronomical Society. Print publication: Issue 2 (2009 March 10). Received 2008 September 10, accepted for publication 2008 December 3. Published 2009 March 10. Rajib Ganguly, Brent Groves, and Phil Maloney graciously helped with comparisons of the data to theoretical models. We are grateful for the helpful suggestions provided by the referee. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through Contract Number 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 theNational Aeronautics and Space Administration and the National Science Foundation.

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August 21, 2023
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