Luminosity Ratio between [O IV] 25.89 um Line and Nuclear Continuum 12 um as Diagnostic for "Buried" AGN

Abstract

We propose new diagnostics that utilize the [O IV] 25.89 $\mu$m and nuclear (subarcsecond scale) 12 $\mu$m luminosity ratio for identifying whether an AGN is deeply `buried' in their surrounding material. Utilizing a sample of 16 absorbed AGNs at redshifts lower than 0.03 in the Swift/BAT catalog observed with Suzaku, we find that AGNs with small scattering fractions ($<$0.5%) tend to show weaker [O IV]-to-12 $\mu$m luminosity ratios than the average of Seyfert 2 galaxies. This suggests that this ratio is a good indicator for identifying buried AGNs. Then, we apply this criterion to 23 local ultra/luminous infrared galaxies (U/LIRGs) in various merger stages hosting AGNs. We find that AGNs in most of mid- to late-stage mergers are buried, while those in earlier stage ones (including non-merger) are not. This result suggests that the fraction of buried AGNs in U/LIRGs increases as the galaxy-galaxy interaction becomes more significant.

8 pages, 4 figures, (accepted in the Astrophysical Journal, ApJ)

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• Hard X-Ray to Radio Multiwavelength SED Analysis of Local U/LIRGs in GOALS Sample with Self-consistent AGN Model Including Polar-dust Component
• NuSTAR Discovery of a Compton-thick Dust-obscured Galaxy WISE J0825+3002
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• CON-quest II. Spatially and spectrally resolved HCN/HCO+ line ratios in local luminous and ultraluminous infrared galaxies
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• Optical IFU Observations of GOALS Sample with KOOLS-IFU on Seimei Telescope: Initial results of 9 U/LIRGs at $z<$ 0.04
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