Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-11-29
Astrophys.J.654:L49-L52,2006
Astronomy and Astrophysics
Astrophysics
5 pages, 3 figures. Accepted for publication in ApJ Letters
Scientific paper
10.1086/511268
We present a new diagnostic diagram for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 micron PAH emission feature and the strength of the 9.7 micron silicate feature. Based on the position in this diagram we classify galaxies into 9 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 non-clumpy obscuration. Spectra of ULIRGs are found along the full length of both branches, reflecting the diverse nature of the ULIRG family.
Armus Lee
Brandl Bernhard R.
Charmandaris Vassilios
Elitzur Moshe
Hao Lei
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