Subaru Adaptive-optics High-spatial-resolution Infrared K- and L'-band
  Imaging Search for Deeply Buried Dual AGNs in Merging Galaxies
  We present the results of infrared K- (2.2 micron) and L'-band (3.8 micron)
high-spatial-resolution (<0.2 arcsec) imaging observations of nearby gas- and
dust-rich infrared luminous merging galaxies, assisted by the adaptive optics
(AO) system on the Subaru 8.2-m telescope. We investigate the presence and
frequency of red K-L' compact sources, which are sensitive indicators of active
galactic nuclei (AGNs), including AGNs that are deeply buried in gas and dust.
We observed 29 merging systems and confirmed at least one AGN in all but one
system. However, luminous dual AGNs were detected in only four of the 29
systems (~14%), despite our method's being sensitive to buried AGNs. For
multiple nuclei sources, we compared the estimated AGN luminosities with
supermassive black hole (SMBH) masses inferred from large aperture K-band
stellar emission photometry in individual nuclei. We found that mass accretion
rates onto SMBHs are significantly different among multiple SMBHs, such that
larger-mass SMBHs generally show higher mass accretion rates when normalized to
SMBH mass. Our results suggest that non-synchronous mass accretion onto SMBHs
in gas- and dust-rich infrared luminous merging galaxies hampers the
observational detection of kiloparsec-scale multiple active SMBHs. This could
explain the significantly smaller detection fraction of kiloparsec-scale dual
AGNs when compared with the number expected from simple theoretical
predictions. Our results also indicate that mass accretion onto SMBHs is
dominated by local conditions, rather than by global galaxy properties,
reinforcing the importance of observations to our understanding of how multiple
SMBHs are activated and acquire mass in gas- and dust-rich merging galaxies.
