Comprehensive Broadband X-ray and Multiwavelength Study of Active
  Galactic Nuclei in Local 57 Ultra/luminous Infrared Galaxies Observed with
  NuSTAR and/or Swift/BAT
  We perform a systematic X-ray spectroscopic analysis of 57 local
ultra/luminous infrared galaxy systems (containing 84 individual galaxies)
observed with Nuclear Spectroscopic Telescope Array and/or Swift/BAT. Combining
soft X-ray data obtained with Chandra, XMM-Newton, Suzaku and/or Swift/XRT, we
identify 40 hard ($>$10 keV) X-ray detected active galactic nuclei (AGNs) and
constrain their torus parameters with the X-ray clumpy torus model XCLUMPY
(Tanimoto et al. 2019). Among the AGNs at $z < 0.03$, for which sample biases
are minimized, the fraction of Compton-thick ($N_{\rm H} \geq 10^{24}$
cm$^{-2}$) AGNs reaches 64$^{+14}_{-15}$% (6/9 sources) in late mergers, while
24$^{+12}_{-10}$% (3/14 sources) in early mergers, consistent with the tendency
reported by Ricci et al. (2017). We find that the bolometric AGN luminosities
derived from the infrared data increase, but the X-ray to bolometric luminosity
ratios decrease, with merger stage. The X-ray weak AGNs in late mergers
ubiquitously show massive outflows at sub-pc to kpc scales. Among them, the
most luminous AGNs ($L_{\rm bol,AGN} \sim 10^{46}$ erg s$^{-1}$) have
relatively small column densities of $\lesssim$10$^{23}$ cm$^{-2}$ and almost
super-Eddington ratios ($\lambda_{\rm Edd} \sim$ 1.0). Their torus covering
factors ($C_{\rm T}^{\rm (22)} \sim 0.6$) are larger than those of Swift/BAT
selected AGNs with similarly high Eddington ratios. These results suggest a
scenario that, in the final stage of mergers, multiphase strong outflows are
produced due to chaotic quasi-spherical inflows and the AGN becomes extremely
X-ray weak and deeply buried due to obscuration by inflowing and/or outflowing
material.
