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| Paper: |
Buried AGNs in LINER-Type ULIRGs |
| Volume: |
290, Active Galactic Nuclei: from Central Engine to Host Galaxy |
| Page: |
509 |
| Authors: |
Imanishi, M. |
| Abstract: |
We report on 3--4 micron spectroscopy of ultraluminous infrared galaxies (ULIRGs). We aim to address the major issue of determining the relative energetic importance of AGN and star formation in ULIRGs, which becomes very difficult if the AGN is buried in a thick dust shell. At 3--4 microns, (1) buried AGN and starburst are distinguishable based on the 3.4 micron carbonaceous dust absorption and the 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission, (2) dust extinction is as low as that at 7--8 microns, and (3) continuum determination, and thereby distinguishing between buried AGN and starburst, is much more secure than the 7.7 micron PAH-based energy diagnostic based on the ISO spectra. All of these advantages combine to make the 3--4 micron diagnostic a very powerful tool to detect ``buried'' AGNs and quantitatively estimate their energetic importance. We successfully find the evidence for energetically important buried AGNs in some ULIRGs classified optically as LINERs (40% of ULIRGs). A theory also predicts that buried AGNs produce LINER-type optical spectra. We argue that, although LINER-type ULIRGs are currently taken to be starburst powered, a significant fraction of these ULIRGs could possess energetically important buried AGNs. This work has been published as Imanishi & Dudley (2000 ApJ 545 701) and Imanishi, Dudley, & Maloney (2001 ApJ 558 L93). |
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