Oral Presentation
Comprehensive Broadband X-ray and Multiwavelength Study of AGNs in 57 Local U/LIRGs Observed with NuSTAR and/or Swift/BAT
Presenter: Satoshi Yamada (Kyoto University)
We perform a systematic X-ray spectroscopic analysis of 57 local ultra/luminous infrared galaxy (U/LIRG) systems (containing 84 individual galaxies) observed with NuSTAR 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 AGNs and constrain their torus parameters with the X-ray clumpy torus model XCLUMPY (Tanimoto+19). Among the AGNs at z < 0.03, for which sample biases are minimized, the fraction of Compton-thick (NH > 10^24 cm^{-2}) AGNs reaches ~64% in late mergers, while ~24% in early mergers, consistent with the tendency reported by Ricci+17 and Ricci+21. 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_{bol,AGN} ~ 10^46 erg/s) have relatively small column densities of <10^23 cm^{-2} and almost super-Eddington ratios (λ_Edd ~ 1.0). Their torus covering factors (C_T^(22) ~ 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 (Yamada+21, ApJS, 257, 61).
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