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Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs

Monfredini, Thiago, Quitián-Lara, Heidy M., Fantuzzi, Felipe, Wolff, Wania, Mendoza, Edgar, Lago, Alexsandre F., Sales, Dinalva A., Pastoriza, Miriani G., Boechat-Roberty, Heloisa M. (2019) Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs. Monthly Notices of the Royal Astronomical Society, 488 (1). pp. 451-469. ISSN 0035-8711. (doi:10.1093/mnras/stz1021) (KAR id:98564)


The infrared signatures of polycyclic aromatic hydrocarbons (PAHs) are observed in a variety of astrophysical objects, including the circumnuclear medium of active galactic nuclei (AGNs). These are sources of highly energetic photons (0.2–10 keV), exposing the PAHs to a harsh environment. In this work, we examined experimentally the photoionization and photostability of naphthalene (C10H8), anthracene (C14H10), 2-methyl-anthracene (C14H9CH3), and pyrene (C16H10) upon interaction with photons of 275, 310, and 2500 eV. The measurements were performed at the Brazilian Synchrotron Light Laboratory using time-of-flight mass-spectrometry. We determined the absolute photoionization and photodissociation cross-sections as a function of the incident photon energy; the production rates of singly, doubly, and triply charged ions; and the molecular half-lives in regions surrounding AGNs. Even considering moderate X-ray optical depth values (τ = 4.45) due to attenuation by the dusty torus, the half-lives are not long enough to account for PAH detection. Our results suggest that a more sophisticated interplay between PAHs and dust grains should be present in order to circumvent molecular destruction. We could not see any significant difference in the half-life values by increasing the size of the PAH carbon backbone, NC, from 10 to 16. However, we show that the multiple photoionization rates are significantly greater than the single ones, irrespective of the AGN source. We suggest that an enrichment of multiply charged ions caused by X-rays can occur in AGNs.

Item Type: Article
DOI/Identification number: 10.1093/mnras/stz1021
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Divisions > Division of Natural Sciences > Chemistry and Forensics
Funders: National Council for Scientific and Technological Development (
Coordenação de Aperfeicoamento de Pessoal de Nível Superior (
Alexander von Humboldt Foundation (
Depositing User: Felipe Fantuzzi
Date Deposited: 30 Nov 2022 23:11 UTC
Last Modified: 04 Mar 2024 18:06 UTC
Resource URI: (The current URI for this page, for reference purposes)

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