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

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, David M. Alexander, Vincenzo Mainieri, Ohad Shemmer, Anton KoekemoerGuido Risaliti

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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 NH, observed fluxes, and absorption-corrected 2-10 keV luminosities LX for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the NH 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 NH can be well explained by the continuum suppression with increasing NH. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of NH for the CDF-S AGN population and present reselected subsamples that are complete with respect to NH. The NH-complete subsamples enable us to decouple the dependences of NH on LX and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average NH and LX of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as fobscured ≈ 0.42 (1+z)0.60.

Original languageEnglish (US)
Article number8
JournalAstrophysical Journal, Supplement Series
Volume232
Issue number1
DOIs
StatePublished - Sep 2017

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occultation
active galactic nuclei
spectral analysis
power law
x rays
spectrum analysis
timescale
luminosity
K lines
distribution
retarding
slopes
continuums
COSMOS
exposure

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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. In: Astrophysical Journal, Supplement Series. 2017 ; Vol. 232, No. 1.
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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 NH, observed fluxes, and absorption-corrected 2-10 keV luminosities LX for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the NH 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 NH can be well explained by the continuum suppression with increasing NH. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of NH for the CDF-S AGN population and present reselected subsamples that are complete with respect to NH. The NH-complete subsamples enable us to decouple the dependences of NH on LX and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average NH and LX of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as fobscured ≈ 0.42 (1+z)0.60.",
author = "Teng Liu and Paolo Tozzi and Wang, {Jun Xian} and Brandt, {William N.} and Cristian Vignali and Yongquan Xue and Schneider, {Donald P.} and Andrea Comastri and Guang Yang and Bauer, {Franz E.} and Maurizio Paolillo and Bin Luo and Roberto Gilli and Wang, {Q. Daniel} and Mauro Giavalisco and Zhiyuan Ji and Alexander, {David M.} and Vincenzo Mainieri and Ohad Shemmer and Anton Koekemoer and Guido Risaliti",
year = "2017",
month = "9",
doi = "10.3847/1538-4365/aa7847",
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Liu, T, Tozzi, P, Wang, JX, Brandt, WN, Vignali, C, Xue, Y, Schneider, DP, Comastri, A, Yang, G, Bauer, FE, Paolillo, M, Luo, B, Gilli, R, Wang, QD, Giavalisco, M, Ji, Z, Alexander, DM, Mainieri, V, Shemmer, O, Koekemoer, A & 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 Series, vol. 232, no. 1, 8. https://doi.org/10.3847/1538-4365/aa7847

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.

In: Astrophysical Journal, Supplement Series, Vol. 232, No. 1, 8, 09.2017.

Research output: Contribution to journalArticle

TY - JOUR

T1 - X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey

T2 - The Distribution, Variability, and Evolutions of AGN Obscuration

AU - Liu, Teng

AU - Tozzi, Paolo

AU - Wang, Jun Xian

AU - Brandt, William N.

AU - Vignali, Cristian

AU - Xue, Yongquan

AU - Schneider, Donald P.

AU - Comastri, Andrea

AU - Yang, Guang

AU - Bauer, Franz E.

AU - Paolillo, Maurizio

AU - Luo, Bin

AU - Gilli, Roberto

AU - Wang, Q. Daniel

AU - Giavalisco, Mauro

AU - Ji, Zhiyuan

AU - Alexander, David M.

AU - Mainieri, Vincenzo

AU - Shemmer, Ohad

AU - Koekemoer, Anton

AU - Risaliti, Guido

PY - 2017/9

Y1 - 2017/9

N2 - 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 NH, observed fluxes, and absorption-corrected 2-10 keV luminosities LX for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the NH 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 NH can be well explained by the continuum suppression with increasing NH. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of NH for the CDF-S AGN population and present reselected subsamples that are complete with respect to NH. The NH-complete subsamples enable us to decouple the dependences of NH on LX and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average NH and LX of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as fobscured ≈ 0.42 (1+z)0.60.

AB - 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 NH, observed fluxes, and absorption-corrected 2-10 keV luminosities LX for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the NH 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 NH can be well explained by the continuum suppression with increasing NH. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of NH for the CDF-S AGN population and present reselected subsamples that are complete with respect to NH. The NH-complete subsamples enable us to decouple the dependences of NH on LX and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average NH and LX of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as fobscured ≈ 0.42 (1+z)0.60.

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UR - http://www.scopus.com/inward/citedby.url?scp=85030266777&partnerID=8YFLogxK

U2 - 10.3847/1538-4365/aa7847

DO - 10.3847/1538-4365/aa7847

M3 - Article

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VL - 232

JO - Astrophysical Journal, Supplement Series

JF - Astrophysical Journal, Supplement Series

SN - 0067-0049

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