Abstract
We present a new diagnostic diagram for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 μm PAH emission feature and the strength of the 9.7 μm silicate feature. Based on the positions in this diagram, we classify galaxies into nine classes ranging from continuum-dominated AGN hot dust spectra and PAH-dominated starburst spectra to absorption-dominated spectra of deeply obscured galactic nuclei. We find that galaxies are systematically distributed along two distinct branches: one of AGN and starburst-dominated spectra and one of deeply obscured nuclei and starburst-dominated spectra. The separation into two branches likely reflects a fundamental difference in the dust geometry in the two sets of sources: clumpy versus nonclumpy obscuration. Spectra of ULIRGs are found along the full length of both branches, reflecting the diverse nature of the ULIRG family.
Document Type
Article
Publication Date
1-1-2007
Digital Object Identifier (DOI)
http://dx.doi.org/10.1086/511268
Repository Citation
Spoon, H. W. W.; Marshall, J. A.; Houck, J. R.; Elitzur, Moshe; Hao, L.; Armus, L.; Brandl, B. R.; and Charmandaris, V., "Mid-Infrared Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width" (2007). Physics and Astronomy Faculty Publications. 208.
https://uknowledge.uky.edu/physastron_facpub/208
Notes/Citation Information
Published in The Astrophysical Journal Letters, v. 654, no. 1, p. L49-L52.
© 2007. The American Astronomical Society. All rights reserved.
The copyright holder has granted permission for posting the article here.