J/MNRAS/443/1999 X-ray spectral analysis of AGNs (Brightman+, 2014)
Compton thick active galactic nuclei in Chandra surveys.
Brightman M., Nandra K., Salvato M. Hsu L.-T., Aird J., Rangel C.
<Mon. Not. R. Astron. Soc. 443, 1999 (2014)>
=2014MNRAS.443.1999B 2014MNRAS.443.1999B
ADC_Keywords: Active gal. nuclei ; QSOs ; X-ray sources
Keywords: galaxies: active, quasars: emission lines, X-rays: galaxies
Abstract:
We present the results from an X-ray spectral analysis of active
galactic nuclei (AGN) in the Chandra Deep Field-South, All-wavelength
Extended Groth-strip International Survey (AEGIS)-Deep X-ray survey
(XD) and Chandra-Cosmic Evolution Surveys (COSMOS), focusing on the
identification and characterization of the most heavily obscured,
Compton thick (CT, NH>1024cm-2) sources. Our sample is comprised
of 3184 X-ray selected extragalactic sources, which has a high rate of
redshift completeness (96.6 per cent), and includes additional
spectroscopic redshifts and improved photometric redshifts over
previous studies. We use spectral models designed for heavily obscured
AGN which self-consistently include all major spectral signatures of
heavy absorption. We validate our spectral fitting method through
simulations, identify CT sources not selected through this method
using X-ray colours and take considerations for the constraints on NH
given the low count nature of many of our sources. After these
considerations, we identify a total of 100 CT AGN with best-fitting NH
>1024cm-2 and NH constrained to be above 1023.5cm-2 at 90 per
cent confidence. These sources cover an intrinsic 2-10keV X-ray
luminosity range of 1042-3x1045erg/s and a redshift range of
z=0.1-4. This sample will enable characterization of these heavily
obscured AGN across cosmic time and to ascertain their cosmological
significance. These survey fields are sites of extensive
multiwavelength coverage, including near-infrared Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS) data and
far-infrared Herschel data, enabling forthcoming investigations into
the host properties of CT AGN. Furthermore, by using the torus models
to test different covering factor scenarios, and by investigating the
inclusion of the soft scattered emission, we find evidence that the
covering factor of the obscuring material decreases with LX for all
redshifts, consistent with the receding torus model, and that this
factor increases with redshift, consistent with an increase in the
obscured fraction towards higher redshifts. The strong relationship
between the parameters of obscuration and LX points towards an origin
intrinsic to the AGN; however, the increase of the covering factor
with redshift may point towards contributions to the obscuration by
the host galaxy. We make NH, {GAMMA} (with uncertainties), observed
X-ray fluxes and intrinsic 2-10keV luminosities for all sources
analysed in this work publicly available in an online catalogue.
Description:
X-ray spectral analysis of all sources in this sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
cdfs.dat 188 549 Data for the Chandra Deep Field South
aegis.dat 183 937 Data for AEGIS-XD
cosmos.dat 173 1761 Data for Chandra COSMOS
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See also:
J/ApJS/184/158 : Chandra COSMOS survey I. (Elvis+, 2009)
J/ApJS/201/30 : The Chandra COSMOS survey. III. (Civano+, 2012)
J/MNRAS/428/3089 : X-ray properties of BzK-selected galaxies (Rangel+, 2013)
Byte-by-byte Description of file: cdfs.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- --- [cdfs4Ms_]
9- 11 I3 --- XID [1/571] X-ray source ID (cdfs4Ms_NNN) (1)
13- 21 F9.6 deg RAdeg Right ascension (J2000.0) of X-ray source (1)
23- 32 F10.6 deg DEdeg Declination (J2000.0) of X-ray source (1)
34- 42 F9.6 deg RAOdeg Right ascension (J2000.0) of Optical/IR
counterpart (2)
44- 53 F10.6 deg DEOdeg Declination (J2000.0) of Optical/IR
counterpart (2)
55- 62 F8.4 --- z ?=-99 Source redshift (2)
64- 70 F7.3 % q_z [0/101] Redshift probability (quality) (G1)
72- 76 I5 ct Xct 0.5-8keV X-ray spectral counts
78 A1 --- Mod [A-D] X-ray spectral model used (G2)
80- 88 F9.6 [cm-2] logNH log(Hydrogen column density)
90- 98 F9.6 [cm-2] b_logNH 90% lower limit on log(NH)
100-108 F9.6 [cm-2] B_logNH 90% upper limit on log(NH)
110-120 F11.8 --- Gamma X-ray power-law index Γ
122-131 F10.7 --- b_Gamma ?=0 90% lower limit on Gamma
133-142 F10.7 --- B_Gamma ?=0 90% upper limit on Gamma
143-153 F11.8 % fscat [0/100]? Scattered fraction
154 A1 --- f_fscat [n] n for not analysed
155-166 F12.9 % e_fscat [0/100]? 90% error on the scattered fraction
168-177 F10.6 [mW/m2] logFX ? log(0.5-8keV observed flux)(ergs/cm2/s)
178 A1 --- f_logFX [I] I for -∞ (FX=0)
179-187 F9.6 [10-7W] logLX ? Intrinsic rest-frame 2-10keV luminosity
(log scale, ergs/s)
188 A1 --- f_logLX [I] I for -∞ (LX=0)
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Note (1): Rangel et al. (2013MNRAS.428.3089R 2013MNRAS.428.3089R, Cat. J/MNRAS/428/3089).
Note (2): from Hsu et al. (submitted).
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Byte-by-byte Description of file: aegis.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- --- [aegis_]
7- 9 I3 --- XID [1/937] X-ray source ID, aegis_NNN (3)
11- 19 F9.5 deg RAdeg Right ascension (J2000.0) of X-ray source (3)
21- 29 F9.6 deg DEdeg Declination (J2000.0) of X-ray source (3)
31- 39 F9.5 deg RAOdeg Right ascension (J2000.0) of Optical/IR
counterpart (3)
41- 49 F9.6 deg DEOdeg Declination (J2000.0) of Optical/IR
counterpart (3)
51- 59 F9.7 --- z Source redshift (3)
61- 63 I3 % q_z [0/101] Redshift probability (quality) (G1)
65- 69 I5 ct Xct 0.5-8keV X-ray spectral counts
71 A1 --- Mod [A-D] X-ray spectral model used
73- 81 F9.6 [cm-2] logNH log(Hydrogen column density)
83- 91 F9.6 [cm-2] b_logNH 90% lower limit on logNH
93-101 F9.6 [cm-2] B_logNH 90% upper limit on logNH
103-112 F10.7 --- Gamma X-ray power-law index Γ
114-123 F10.7 --- b_Gamma ?=0 90% lower limit on Gamma
125-134 F10.7 --- B_Gamma ?=0 90% upper limit on Gamma
136-147 F12.9 % fscat [0/100]? Scattered fraction
149-161 F13.10 % e_fscat [0/100]? 90% error on the scattered fraction
163-173 F11.7 [mW/m2] logFX log(0.5-8keV observed flux) (ergs/cm2/s)
174-182 F9.6 [10-7W] logLX ? Intrinsic rest-frame 2-10keV luminosity
(log scale, ergs/s)
183 A1 --- n_logLX [I] I for -∞ (LX=0)
-------------------------------------------------------------------------------
Note (3): from Nandra et al. (submitted).
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Byte-by-byte Description of file: cosmos.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- XID [1/22962] X-ray source XID (4)
7- 15 F9.5 deg RAdeg Right ascension (J2000.0) of X-ray source (4)
17- 23 F7.5 deg DEdeg Declination (J2000.0) of X-ray source (4)
25- 33 F9.5 deg RAOdeg Right ascension (J2000.0) of Optical/IR
counterpart (5)
35- 41 F7.5 deg DEOdeg Declination (J2000.0) of Optical/IR
counterpart (5)
43- 49 F7.3 --- z ?=-99 Source redshift (5)
51- 53 I3 % q_z [0/101] Redshift probability (quality) (G1)
55- 58 I4 ct Xct 0.5-8keV X-ray spectral counts
60 A1 --- Mod [A-D] X-ray spectral model used
62- 70 F9.6 [cm-2] logNH ? log(Hydrogen column density)
71 A1 --- n_logNH [I] I for -∞ (NH=0)
72- 80 F9.6 [cm-2] b_logNH 90% lower limit on logNH
82- 90 F9.6 [cm-2] B_logNH ? 90% upper limit on logNH
91 A1 --- nBlogNH [I] I for -∞
92-101 F10.7 --- Gamma ? X-ray power-law index Γ
103-112 F10.7 --- b_Gamma ?=0 90% lower limit on Gamma
114-123 F10.7 --- B_Gamma ?=0 90% upper limit on Gamma
124-137 E14.9 % fscat [0/100]? Scattered fraction
138 A1 --- f_fscat [n] n for not analyzed
139-151 E13.8 % e_fscat [0/100]? 90% error on the scattered fraction
153-162 F10.6 [mW/m2] logFX ? log(0.5-8keV observed flux) (ergs/cm2/s)
163 A1 --- n_logFX [I] I for -∞ (FX=0)
164-172 F9.6 [10-7W] logLX ? Intrinsic rest-frame 2-10keV luminosity
(log scale, ergs/s)
173 A1 --- n_logLX [I] I for -∞ (LX=0)
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Note (4): from Elvis et al. (2009ApJS..184..158E 2009ApJS..184..158E, Cat. J/ApJS/184/158).
Note (5): from Civano et al. (2012ApJS..201...30C 2012ApJS..201...30C, Cat. J/ApJS/201/30).
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Global notes:
Note (G1): Redshift quality: from 0=star/photometric redshift,
to 101=spectroscopic redshift
Note (G2): The models are:
A = The torus model of Brightman & Nandra 2011 (J/MNRAS/413/1206) with
a fixed opening angle of 60°, and edge on orientation, accompanied
by a scattered power-law with Γscatt fixed to the value of the
primary power-law. This model has four free parameters: NH, Γ,
and the normalisations of the power-laws, A1 and A2
B = The torus model of Brightman & Nandra 2011 (J/MNRAS/413/1206) with
a fixed opening angle of 30°, and edge on orientation, accompanied
by a scattered power-law with Γscatt fixed to the value of the
primary power-law. This model has four free parameters, NH, Γ,
and the normalisations of the power-laws, A1 and A2
C = The spherical model of Brightman & Nandra 2011 (J/MNRAS/413/1206),
a scenario in which the X-ray source is completely covered with 4π
steradians of obscuring material. This model has three free parameters
NH, Γ, and the normalisation of the power-laws, A1. No
scattered component iw included for this model as it represents the
case where there is no escape route for the primary radiation to be
scattered into the line of sight.
D = simple power-law model, with two free parameters: the power-law index
Γ, and the normalisation, A1, representing unobscured X-ray
emission.
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Acknowledgements:
Murray Brightman, murray(at)srl.caltech.edu
(End) Patricia Vannier [CDS] 05-Sep-2014