Chandra X-ray and Hubble Space Telescope Imaging of Optically Selected
  Kiloparsec-Scale Binary Active Galactic Nuclei II: Host Galaxy Morphology and
  AGN Activity
  Binary active galactic nuclei (AGNs) provide clues to how gas-rich mergers
trigger and fuel AGNs and how supermassive black hole (SMBH) pairs evolve in a
gas-rich environment. While significant effort has been invested in their
identification, the detailed properties of binary AGNs and their host galaxies
are still poorly constrained. In a companion paper, we examined the nature of
ionizing sources in the double nuclei of four kpc-scale binary AGNs with
redshifts between 0.1~0.2. Here, we present their host galaxy morphology based
on F336W (U-band) and F105W (Y-band) images taken by the Wide Field Camera 3
(WFC3) onboard the Hubble Space Telescope. Our targets have double-peaked
narrow emission lines and were confirmed to host binary AGNs with follow up
observations. We find that kpc-scale binary AGNs occur in galaxy mergers with
diverse morphological types. There are three major mergers with intermediate
morphologies and a minor merger with a dominant disk component. We estimate the
masses of the SMBHs from their host bulge stellar masses and obtain Eddington
ratios for each AGN. Compared with a representative control sample drawn at the
same redshift and stellar mass, the AGN luminosities and Eddington ratios of
our binary AGNs are similar to those of single AGNs. The U-Y color maps
indicate that clumpy star forming regions could significantly affect the X-ray
detection of binary AGNs, e.g., the hardness ratio. Considering the weak X-ray
emission in AGNs triggered in merger systems, we suggest that samples of X-ray
selected AGNs may be biased against gas-rich mergers.
