A High-resolution Search for Dual Active Galactic Nucleus Candidates in Mergers: A Preselection Strategy Using Keck Adaptive Optics
August 2026 • 2026ApJ..1006..251V
Abstract • Accreting supermassive black holes (SMBHs) in galaxy mergers with separations <1 kpc are crucial for understanding SMBH growth, galaxy evolution, and SMBH binary evolution. Despite their importance, few are known, and most have been discovered serendipitously. In this work, we develop and test a method to systematically preselect advanced mergers likely to contain unresolved subkiloparsec nuclear substructure and dual active galactic nucleus (AGN) candidates for follow-up spectroscopy. By exploiting the survey area and astrometric precision of the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS), we identify 46 advanced mergers that have red WISE colors (W1 − W2 > 0.5) indicative of accretion activity and significant subarcsecond offsets between their optical and infrared coordinates. We conduct high-resolution adaptive optics observations with the Keck Near Infrared Camera 2 in the Kp band (2.124 μm, ∆λ = 0.351 μm) to search for unresolved substructure suggested by these offsets. We find that 20/46 (43.5%) of the sample show substructure tracing the SDSS/WISE offset. When restricted to detections of compact nuclear components with separations <3 kpc, we achieve a detection rate of 34.8%, a higher yield than previous preselection techniques, such as double-peaked [O III] or hard-X-ray selection. These results demonstrate that the SDSS/WISE offset method provides an efficient pathway for identifying late-stage mergers and dual-AGN candidates for spectroscopic confirmation. Archival optical Hubble Space Telescope imaging reveals that substructure identified with Keck is often missed in the optical or erroneously identified, due to partial obscuration, underscoring the importance of infrared studies of late-stage mergers.
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