Observational analysis confirms the Iwasawa–Taniguchi effect in Compton-thick AGN, indicating reduced Fe Kα production efficiency in extended emissions.
The anti-correlation between the equivalent width of the neutral narrow Fe Kα line and the 2–10 keV luminosity (the Iwasawa–Taniguchi effect) in the nuclear regions of active galactic nuclei has been debated in recent years. With the high angular resolution of Chandra, an increasing number of Compton-thick sources have been found to show extended narrow Fe Kα emission on scales from tens of parsecs to kiloparsecs, attributed to reprocessing of nuclear radiation by surrounding Compton-thick material. We analyze eight Compton-thick sources with prominent extended Fe Kα emission. We confirm the Iwasawa–Taniguchi effect in the extended component relative to the reflection spectrum, with a steeper slope, indicating reduced production efficiency of neutral Fe Kα photon outside the nucleus. Both the reflection spectrum and Fe Kα luminosities correlate positively with intrinsic AGN luminosity, suggesting that the nucleus drives the extended emission. Finally, we find a linear relationship between redshift and the equivalent width of the nuclear Fe Kα line, with no such trend in the extended component.
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Chen et al. (2025) studied this question.
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