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

July 2006 • 2006ApJ...646..161D

Authors • Dale, D. A. • Smith, J. D. T. • Armus, L. • Buckalew, B. A. • Helou, G. • Kennicutt, R. C., Jr. • Moustakas, J. • Roussel, H. • Sheth, K. • Bendo, G. J. • Calzetti, D. • Draine, B. T. • Engelbracht, C. W. • Gordon, K. D. • Hollenbach, D. J. • Jarrett, T. H. • Kewley, L. J. • Leitherer, C. • Li, A. • Malhotra, S. • Murphy, E. J. • 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.

Links

• PREPRINT http://arxiv.org/abs/astro-ph/0604007
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2006ApJ...646..161D
• ELECTR https://doi.org/10.1086%2F504835
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2006ApJ...646..161D
• PDF https://stacks.iop.org/0004-637X/646/161/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/646/161
• DATA https://irsa.ipac.caltech.edu/bibdata/2006/D/2006ApJ...646..161D.html
• SPIRES http://inspirehep.net/search?p=find+eprint+astro-ph/0604007