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X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

Liu, Teng; Tozzi, Paolo; Wang, Jun-Xian; Brandt, William N.; Vignali, Cristian; Xue, Yongquan; Schneider, Donald P.; Comastri, Andrea; Yang, Guang; Bauer, Franz E.; Paolillo, Maurizio; Luo, Bin; Gilli, Roberto; Wang, Q. Daniel; Giavalisco, Mauro; Ji, Zhiyuan; Alexander, David M; Mainieri, Vincenzo; Shemmer, Ohad; Koekemoer, Anton; Risaliti, Guido

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration Thumbnail


Authors

Teng Liu

Paolo Tozzi

Jun-Xian Wang

William N. Brandt

Cristian Vignali

Yongquan Xue

Donald P. Schneider

Andrea Comastri

Guang Yang

Franz E. Bauer

Maurizio Paolillo

Bin Luo

Roberto Gilli

Q. Daniel Wang

Mauro Giavalisco

Zhiyuan Ji

Vincenzo Mainieri

Ohad Shemmer

Anton Koekemoer

Guido Risaliti



Abstract

We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2–21 months. With this approach, we not only present the power-law slopes, column densities ${N}_{{\rm{H}}}$, observed fluxes, and absorption-corrected 2–10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the ${N}_{{\rm{H}}}$ variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and ${N}_{{\rm{H}}}$ can be well explained by the continuum suppression with increasing ${N}_{{\rm{H}}}$. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of ${N}_{{\rm{H}}}$ for the CDF-S AGN population and present reselected subsamples that are complete with respect to ${N}_{{\rm{H}}}$. The ${N}_{{\rm{H}}}$-complete subsamples enable us to decouple the dependences of ${N}_{{\rm{H}}}$ on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average ${N}_{{\rm{H}}}$ and L X of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as ${f}_{\mathrm{obscured}}\approx 0.42\ {(1+z)}^{0.60}$.

Citation

Liu, T., Tozzi, P., Wang, J., Brandt, W. N., Vignali, C., Xue, Y., …Risaliti, G. (2017). X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration. Astrophysical Journal Supplement, 232(1), Article 8. https://doi.org/10.3847/1538-4365/aa7847

Journal Article Type Article
Acceptance Date Jun 6, 2017
Online Publication Date Aug 31, 2017
Publication Date Aug 31, 2017
Deposit Date Oct 12, 2017
Publicly Available Date Oct 12, 2017
Journal Astrophysical Journal Supplement
Print ISSN 0067-0049
Electronic ISSN 1538-4365
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 232
Issue 1
Article Number 8
DOI https://doi.org/10.3847/1538-4365/aa7847

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Copyright Statement
© 2017. The American Astronomical Society. All rights reserved.





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