Hard X-Ray Irradiation Potentially Drives Negative AGN Feedback by Altering Molecular Gas Properties
Journal article, 2021

To investigate the role of active galactic nucleus (AGN) X-ray irradiation on the interstellar medium (ISM), we systematically analyzed Chandra and Atacama Large Millimeter/submillimeter Array CO (J = 2-1) data for 26 hard X-ray (>10 keV) selected AGNs at redshifts below 0.05. While Chandra unveils the distribution of X-ray-irradiated gas via Fe-K alpha emission, the CO (J = 2-1) observations reveal that of cold molecular gas. At high resolutions less than or similar to 1 '', we derive Fe-K alpha and CO (J = 2-1) maps for the nuclear 2 '' region and for the external annular region of 2 ''-4 '', where 2 '' is similar to 100-600 pc for most of our AGNs. First, focusing on the external regions, we find the Fe-K alpha emission for six AGNs above 2 sigma. Their large equivalent widths (greater than or similar to 1 keV) suggest a fluorescent process as their origin. Moreover, by comparing the 6-7 keV/3-6 keV ratio, as a proxy of Fe-K alpha, and CO (J = 2-1) images for three AGNs with the highest significant Fe-K alpha detections, we find a possible spatial separation. These suggest the presence of X-ray-irradiated ISM and the change in the ISM properties. Next, examining the nuclear regions, we find that (1) the 20-50 keV luminosity increases with the CO (J = 2-1) luminosity; (2) the ratio of CO (J = 2-1)/HCN (J = 1-0) luminosities increases with 20-50 keV luminosity, suggesting a decrease in the dense gas fraction with X-ray luminosity; and (3) the Fe-K alpha-to-X-ray continuum luminosity ratio decreases with the molecular gas mass. This may be explained by a negative AGN feedback scenario: the mass accretion rate increases with gas mass, and simultaneously, the AGN evaporates a portion of the gas, which possibly affects star formation.


Taiki Kawamuro

National Astronomical Observatory of Japan

Diego Portales University

Claudio Ricci

Diego Portales University

Beijing University of Technology

Takuma Izumi

The Graduate University for Advanced Studies (SOKENDAI)

National Astronomical Observatory of Japan

Masatoshi Imanishi

National Astronomical Observatory of Japan

The Graduate University for Advanced Studies (SOKENDAI)

Shunsuke Baba

National Astronomical Observatory of Japan

Dieu D. Nguyen

Vietnam National University

Kyoko Onishi

Astronomy and plasmaphysics 2

Astrophysical Journal, Supplement Series

0067-0049 (ISSN) 1538-4365 (eISSN)

Vol. 257 2 64

Subject Categories

Subatomic Physics

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics



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