Journal
ASTROPHYSICAL JOURNAL
Volume 733, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/733/2/103
Keywords
galaxies: active; galaxies: formation; galaxies: interactions; galaxies: nuclei; quasars: emission lines
Categories
Funding
- W. M. Keck Foundation
- NASA [NNX08AJ28G, GO9-0114]
- NSF [AST-0909182]
- Ajax Foundation
- NASA [100898, NNX08AJ28G] Funding Source: Federal RePORTER
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [909182] Funding Source: National Science Foundation
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As a natural consequence of galaxy mergers, binary active galactic nuclei (AGNs) should be commonplace. Nevertheless, observational confirmations are rare, especially for binaries with separations less than 10 kpc. Such a system may show two sets of narrow emission lines in a single spectrum owing to the orbital motion of the binary. We have obtained high-resolution near-infrared images of 50 double-peaked [O III]lambda 5007 AGNs with the Keck II laser guide star adaptive optics system. The Sloan Digital Sky Survey sample is compiled from the literature and consists of 17 type-1 AGNs between 0.18 < z < 0.56 and 33 type-2 AGNs between 0.03 < z < 0.24. The new images reveal eight type-1 and eight type-2 sources that are apparently undergoing mergers. These are strong candidates of kpc-scale binary AGNs because they show multiple components separated between 0.6 and 12 kpc and often disturbed morphologies. Because most of the type-1s are at higher redshifts than the type-2s, the higher merger fraction of type-1s (47% +/- 20%) compared to that of type-2s (24% +/- 10%) can be attributed to the general evolution of galaxy merger fraction with redshift. Furthermore, we show that AGN mergers are outliers of the M-BH-sigma(*) relation because of overestimated stellar velocity dispersions, illustrating the importance of removing mergers from the samples defining the M-BH-sigma(*) relations. Finally, we find that the emission-line properties are indistinguishable for spatially resolved and unresolved sources, emphasizing that scenarios involving a single AGN can produce the same double-peaked line profiles and they account for at least 70% of the double-peaked [O III] AGNs.
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