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Chandra Observations of Excess Fe Kα Line Emission in Galaxies with High Star Formation Rates: X-Ray Reflection on Galaxy Scales?

Yan, Wei; Hickox, Ryan C.; Chen, Chien-Ting J.; Ricci, Claudio; Masini, Alberto; Bauer, Franz E.; Alexander, David M.

Chandra Observations of Excess Fe Kα Line Emission in Galaxies with High Star Formation Rates: X-Ray Reflection on Galaxy Scales? Thumbnail


Authors

Wei Yan

Ryan C. Hickox

Chien-Ting J. Chen

Claudio Ricci

Alberto Masini

Franz E. Bauer



Abstract

In active galactic nuclei (AGNs), fluorescent Fe Kα (iron) line emission is generally interpreted as originating from obscuring material around a supermassive black hole on the scale of a few parsecs. However, recent Chandra studies indicate the existence of iron line emission extending to kiloparsec scales in the host galaxy. The connection between iron line emission and large-scale material can be spatially resolved directly only in nearby galaxies, but could be inferred in more distant AGNs by a connection between line emission and star-forming gas and dust that is more extended than the parsec-scale torus. Here we present the results from a stacking analysis and X-ray spectral fitting performed on sources in the Chandra Deep Field South (CDFS) 7 Ms observations. From the deep stacked spectra, we select sources with stellar mass log 10 M M > * ( )  at 0.5 < z < 2, obtaining 25 sources with high-infrared (IR) luminosity (star formation rate, SFRFIR … 17 M☉ yr−1 ) and 32 sources below this threshold. We find that the equivalent width (EW) of the iron line EW(Fe) is a factor of three higher with 3σ significance for high-IR luminosity measured from Herschel observations, indicating a connection between iron line emission and star-forming material on galaxy scales. We show that there is no significant dependence of the EW(Fe) on M* or X-ray luminosity, suggesting that the reflection of AGN X-ray emission over large scales in their host galaxies may be widespread.

Journal Article Type Article
Acceptance Date Apr 20, 2021
Online Publication Date Jun 17, 2021
Publication Date 2021-06
Deposit Date Aug 23, 2021
Publicly Available Date Aug 23, 2021
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 914
Issue 2
Article Number 83
DOI https://doi.org/10.3847/1538-4357/abfaa0
Public URL https://durham-repository.worktribe.com/output/1242502

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© 2021. The American Astronomical Society. All rights reserved.






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