We have analyzed the broadband X-ray spectra of active galactic nuclei ( AGNs ) in two “ non-merging ” luminous infrared galaxies ( LIRGs ) UGC 2608 and NGC 5135 , utilizing the data of NuSTAR , Suzaku , XMM-Newton , and Chandra .
Applying the X-ray clumpy-torus model ( XCLUMPY : \citealt Tanimoto2019 ) , we find that both sources have similar spectra characterized by Compton-thick ( CT ) absorption ( N _ { H } \sim 5–7 \times 10 ^ { 24 } cm ^ { -2 } ) and small torus angular width ( \sigma < 20 \degr ) .
The intrinsic 2–10 keV luminosities are 3.9 ^ { +2.2 } _ { -1.7 } \times 10 ^ { 43 } erg s ^ { -1 } ( UGC 2608 ) and 2.0 ^ { +3.3 } _ { -1.0 } \times 10 ^ { 43 } erg s ^ { -1 } ( NGC 5135 ) .
The [ \ion O4 ] -to-nuclear-12 \mu m luminosity ratios are larger than those of typical Seyferts , which are consistent with the torus covering factors ( C _ { T } \lesssim 0.7 ) estimated from the torus angular widths and column densities by X-ray spectroscopy .
The torus covering factors and Eddington ratios ( \lambda _ { Edd } \sim 0.1 ) follow the relation found by \citet Ricci2017cNature for local AGNs , implying that their tori become geometrically thin due to significant radiation pressure of the AGN that blows out some part of the tori .
These results indicate that the CT AGNs in these “ non-merger ” LIRGs are just a normal AGN population seen edge-on through a large line-of-sight column density .
They are in contrast to the buried CT AGNs in late-stage mergers that have large torus covering factors even at large Eddington ratios .