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Journal articles
X-ray Spectral Constraints for $z\approx$2 Massive Galaxies: The Identification of Reflection-Dominated Active Galactic Nuclei
D. M. Alexander
1
F. E. Bauer
2
W. N. Brandt
3, 4
Emanuele Daddi
5
R. C. Hickox
1, 6
B. D. Lehmer
7, 8
B. Luo
3, 4
Y. Q. Xue
3, 4
M. Young
3, 4
A. Comastri
9
A. del Moro
1
A. C. Fabian
10
R. Gilli
9
A. D. Goulding
1, 6
V. Mainieri
11
J. R. Mullaney
5
M. Paolillo
12
D. A. Rafferty
3
D. P. Schneider
3
O. Shemmer
13
C. Vignali
14
C. Vignali 14
Author
1
Department of Physics (Durham University, South road, Durham, DH1 - United Kingdom)
- Durham University (Stockton Road, Durham DH1 3LE - United Kingdom)
2
Departamento de Astronomía y Astrofísica [Santiago] (Casilla 306, Santiago 22 - Chile)
- UC - Pontificia Universidad Católica de Chile (Casilla 306, Santiago 22 - Chile)
3
Department of Astronomy and Astrophysics [PennState] (Pennsylvania State University, University Park, PA 16802, USA - United States)
- Penn State - Pennsylvania State University (201 Old Main, University Park, Pennsylvania 16802 - United States)
- Penn State System (Pennsylvania, PA, USA, Etats-Unis - United States)
4
Institute for Gravitation and the Cosmos [PennState] (The Pennsylvania State University, University Park, PA 16802, USA - United States)
- Penn State - Pennsylvania State University (201 Old Main, University Park, Pennsylvania 16802 - United States)
- Penn State System (Pennsylvania, PA, USA, Etats-Unis - United States)
5
AIM (UMR_7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation (AIM - UMR 7158 - UMR E 9005,
ex "Astrophysique Interactions Multi-échelles",
Service d'astrophysique,
CEA/Saclay,
Orme des Merisiers
F-91191 GIF SUR YVETTE CEDEX - France)
- CNRS - Centre National de la Recherche Scientifique : UMR_7158 (France)
- INSU - CNRS - Institut national des sciences de l'Univers (INSU-CNRS 3 rue Michel-Ange, 75794 Paris Cedex 16 - France)
- CEA - Commissariat à l'énergie atomique et aux énergies alternatives : UMR_E_9005 (Centre de Saclay Centre de Grenoble Centre de Cadarache etc - France)
- UPD7 - Université Paris Diderot - Paris 7 : UMR_7158 (5 rue Thomas-Mann - 75205 Paris cedex 13 - France)
6
CfA - Harvard-Smithsonian Center for Astrophysics (60 Garden Street, Cambridge, MA 02138, USA - United States)
- Harvard University [Cambridge] (Massachusetts Hall, Cambridge, MA 02138 - United States)
- Smithsonian Institution (PO Box 37012, Washington, DC 20013-7012 - United States)
7
JHU - Johns Hopkins University (Baltimore, Maryland 410-516-8000 - United States)
8
GSFC - NASA Goddard Space Flight Center (Greenbelt, MD 20771 - United States)
9
OABO - INAF - Osservatorio Astronomico di Bologna (via Ranzani 1, 40127 Bologna - Italy)
- INAF - Istituto Nazionale di Astrofisica (Viale del Parco Mellini 84, 00136 Roma - Italy)
10
Institute of Astronomy [Cambridge] ( Madingley Rd, Cambridge CB3 0HA - United Kingdom)
- CAM - University of Cambridge [UK] (The Old Schools, Trinity Lane, Cambridge CB2 1TN - United Kingdom)
11
ESO - European Southern Observatory (Karl-Schwarzchild Str. 2 D-85748 Garching bei Munchen - Germany)
12
Dipartimento di Scienze Fisiche [Naples] (Università degli Studi di Napoli Federico II - Complesso Universitario di Monte Sant'Angelo - Via Cinthia, I-80126, Napoli - Italy)
- Università degli studi di Napoli Federico II (Corso Umberto I 40 - 80138 Napoli - Italy)
13
Department of Physics (Department of Physics, University of North Texas, Denton, TX 76203, USA - United States)
- UNT - University of North Texas (P.O. Box 311277 Denton, Texas 76203-1277 - United States)
14
Dipartimento di Astronomia, Universita degli Studi di Bologna (Italy)
- UNIBO - Alma Mater Studiorum Università di Bologna [Bologna] (Via Zamboni, 33 - 40126 Bologna - Italy)
Abstract : We use the 4 Ms $Chandra$ Deep Field-South (CDF-S) survey to place direct constraints on the ubiquity of z ≈ 2
heavily obscured active galactic nuclei (AGNs) in K < 22 $BzK$-selected galaxies. Forty-seven (≈21%) of the 222
$BzK$-selected galaxies in the central region of the CDF-S are detected at X-ray energies, 11 (≈5%) of which have
hard X-ray spectral slopes (Γ $^<_\sim$ 1), indicating the presence of heavily obscured AGN activity H$^<_\sim$3×10$^{23}$ cm$^{−2}$).
The other 36 X-ray detected $BzK$ galaxies appear to be relatively unobscured AGNs and starburst galaxies; we use
X-ray variability analyses over a rest-frame baseline of ≈3 years to further confirm the presence of AGN activity in
many of these systems. The majority (7 out of 11) of the heavily obscured AGNs have excess infrared emission over
that expected from star formation (termed “infrared-excess galaxies”). However, we find that X-ray detected heavily
obscured AGNs only comprise ≈25% of the infrared-excess galaxy population, which is otherwise composed of
relatively unobscured AGNs and starburst galaxies. We find that the typical X-ray spectrum of the heavily obscured
AGNs is better characterized by a pure reflection model than an absorbed power-law model, suggesting extreme
Compton-thick absorption (NH$^<_\sim$10$^{24}$ cm$^{−2}$) in some systems. We verify this result by producing a composite rest-frame 2–20 keV spectrum, which has a similar shape as a reflection-dominated X-ray spectrum and reveals
an emission feature at rest-frame energy ≈6.4 keV, likely to be due to Fe K. These heavily obscured AGNs are
likely to be the distant analogs of the reflection-dominated AGNs recently identified at z ≈ 0 with >10 keV
observatories. On the basis of these analyses, we estimate the space density for typical (intrinsic X-ray luminosities
of $L_{2−10 keV}$$^<_\sim$10$^{43}$erg s$^{−1}$) heavily obscured and Compton-thick AGNs at z ≈ 2. Our space-density constraints are conservative lower limits but they are already consistent with the range of predictions from X-ray background models
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Journal articles
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Submitted on : Tuesday, November 3, 2020 - 12:22:03 PM
Last modification on : Monday, January 11, 2021 - 10:30:04 AM
Long-term archiving on: : Thursday, February 4, 2021 - 6:29:28 PM
Contributor : Bruno Savelli <>
Submitted on : Tuesday, November 3, 2020 - 12:22:03 PM
Last modification on : Monday, January 11, 2021 - 10:30:04 AM
Long-term archiving on: : Thursday, February 4, 2021 - 6:29:28 PM
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Identifiers
- HAL Id : cea-00998762, version 1
- ARXIV : 1106.1443
- DOI : 10.1088/0004-637X/738/1/44
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CEA | UP-SCIENCES | UNIV-PARIS | USPC | CEA-DRF | DSM-IRFU | IRFU-AIM | INSU | CNRS | UNIV-PARIS7
Citation
D. M. Alexander, F. E. Bauer, W. N. Brandt, Emanuele Daddi, R. C. Hickox, et al.. X-ray Spectral Constraints for $z\approx$2 Massive Galaxies: The Identification of Reflection-Dominated Active Galactic Nuclei. The Astrophysical Journal, American Astronomical Society, 2011, 738 (1), pp.44. ⟨10.1088/0004-637X/738/1/44⟩. ⟨cea-00998762⟩
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