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Volume 11
Issue 10
10.3390/universe11100348
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission

by
Jia Chen
1,
Huili Yi
1,*,
Chengchao Liu
1,
Shenfang Ye
1 and
Shuangxi Yi
2
1
School of Physics and Electronic Engineering, Linyi University, Linyi 276000, China
2
School of Physics and Physical Engineering, Qufu Normal University, Qufu 273165, China
*
Author to whom correspondence should be addressed.
Universe 2025, 11(10), 348; https://doi.org/10.3390/universe11100348 (registering DOI)
Submission received: 15 August 2025 / Revised: 6 October 2025 / Accepted: 8 October 2025 / Published: 18 October 2025
(This article belongs to the Special Issue 10th Anniversary of Universe: Galaxies and Their Black Holes)
Versions Notes

Abstract

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.
Keywords: active galaxies; Iwasawa-Taniguchi effect; Compton-thick; equivalent width; Fe Kα line active galaxies; Iwasawa-Taniguchi effect; Compton-thick; equivalent width; Fe Kα line

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MDPI and ACS Style

Chen, J.; Yi, H.; Liu, C.; Ye, S.; Yi, S. The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission. Universe 2025, 11, 348. https://doi.org/10.3390/universe11100348

AMA Style

Chen J, Yi H, Liu C, Ye S, Yi S. The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission. Universe. 2025; 11(10):348. https://doi.org/10.3390/universe11100348

Chicago/Turabian Style

Chen, Jia, Huili Yi, Chengchao Liu, Shenfang Ye, and Shuangxi Yi. 2025. "The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission" Universe 11, no. 10: 348. https://doi.org/10.3390/universe11100348

APA Style

Chen, J., Yi, H., Liu, C., Ye, S., & Yi, S. (2025). The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission. Universe, 11(10), 348. https://doi.org/10.3390/universe11100348

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