J/ApJ/877/5 Chandra DF obscured & Compton-thick AGNs. I. Variability (Li+, 2019)
Piercing through highly obscured and Compton-thick AGNs in the Chandra Deep
Fields.
I. X-ray spectral and long-term variability analyses.
Li J., Xue Y., Sun M., Liu T., Vito F., Brandt W.N., Hughes T.M., Yang G.,
Tozzi P., Zhu S., Zheng X., Luo B., Chen C.-T., Vignali C., Gilli R., Shu X.
<Astrophys. J., 877, 5 (2019)>
=2019ApJ...877....5L 2019ApJ...877....5L
ADC_Keywords: Active gal. nuclei; X-ray sources; Redshifts
Keywords: galaxies: active ; galaxies: nuclei ; quasars: general ;
X-rays: galaxies
Abstract:
We present a detailed X-ray spectral analysis of 1152 active galactic
nuclei (AGNs) selected in the Chandra Deep Fields (CDFs), in order to
identify highly obscured AGNs (NH>1023cm-2). By fitting spectra
with physical models, 436 (38%) sources with LX>1042erg/s are
confirmed to be highly obscured, including 102 Compton-thick (CT)
candidates. We propose a new hardness ratio measure of the obscuration
level that can be used to select highly obscured AGN candidates. The
completeness and accuracy of applying this method to our AGNs are 88%
and 80%, respectively. The observed log N-log S relation favors cosmic
X-ray background models that predict moderate (i.e., between
optimistic and pessimistic) CT number counts. Nineteen percent (6/31)
of our highly obscured AGNs that have optical classifications are
labeled as broad-line AGNs, suggesting that, at least for part of the
AGN population, the heavy X-ray obscuration is largely a line-of-sight
effect, i.e., some high column density clouds on various scales (but
not necessarily a dust-enshrouded torus) along our sight line may
obscure the compact X-ray emitter. After correcting for several
observational biases, we obtain the intrinsic NH distribution and
its evolution. The CT/highly obscured fraction is roughly 52% and is
consistent with no evident redshift evolution. We also perform
long-term (∼17yr in the observed frame) variability analyses for
31 sources with the largest number of counts available. Among them,
17 sources show flux variabilities: 31% (5/17) are caused by the
change of NH, 53% (9/17) are caused by the intrinsic luminosity
variability, 6% (1/17) are driven by both effects, and 2 are not
classified owing to large spectral fitting errors.
Description:
This work is based on the Chandra data in the 7Ms CDF-S main-source
catalog (Luo+ 2017, J/ApJS/228/2) and the 2Ms CDF-N main-source
catalog (Xue+ 2016, J/ApJS/224/15).
The source spectra from individual observations were extracted using
the ACIS Extract (AE) software package (Broos+ 2010ApJ...714.1582B 2010ApJ...714.1582B).
Throughout this paper, we adopt a Galactic column density of
NH=8.8x1019cm-2 for the CDF-S and NH=1.6x1020cm-2 for the
CDF-N (Stark+ 1992, VIII/28). We adopt cosmological parameters of
H0=70.0km/s/Mpc, ΩM=0.30, and ΩΛ=0.70.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 100 436 X-ray spectral fitting results for highly
obscured AGNs
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
VIII/10 : Bell Laboratories H I Profiles (Stark+ 1992)
VIII/28 : Bell Laboratories H I Survey (Stark+ 1992)
J/ApJS/79/77 : Bell Lab. H I Survey - High Velocity Clouds (Stark+ 1992)
J/AJ/126/539 : The Chandra Deep Fields North and South (Alexander+, 2003)
J/A+A/409/79 : HELLAS2XMM survey. IV. (Fiore+, 2003)
J/ApJS/155/73 : Phot. redshifts of X-ray sources in CDF-S (Zheng+, 2004)
J/A+A/451/457 : X-ray properties of AGN in CDFS (Tozzi+, 2006)
J/ApJ/642/673 : IR-selected obscured AGN candidates (Polletta+, 2006)
J/ApJ/660/167 : Spitzer AGN candidates in CDFN (Donley+, 2007)
J/A+A/488/73 : Variability-selected AGN in Chandra DFS (Trevese+, 2008)
J/A+A/497/81 : Variability-selected AGN in CDFS (Boutsia+, 2009)
J/ApJ/693/1713 : Spectroscopy of X-ray sources in ECDF-S (Treister+, 2009)
J/ApJS/191/124 : Opt. spectroscopy of ECDF-S X-ray sources (Silverman+, 2010)
J/MNRAS/413/1206 : XMM survey of 12um selected galaxies (Brightman+, 2011)
J/ApJ/728/58 : Swift-BAT survey of AGNs (Burlon+, 2011)
J/A+A/530/A42 : X-ray properties of AGNs in XBS (Corral+, 2011)
J/ApJ/740/37 : Obscured AGN at z∼0.5-1 in the CDFS (Luo+, 2011)
J/ApJ/742/61 : Phot. redshift of AGNs from XMM- & C-COSMOS (Salvato+ 2011)
J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)
J/ApJ/748/124 : AGN X-ray variability in the 4Ms catalog (Young+, 2012)
J/ApJS/207/19 : Swift-BAT 2004-2010 hard X-ray survey (Baumgartner+, 2013)
J/A+A/555/A42 : The XMM-CDFS catalogues (Ranalli+, 2013)
J/MNRAS/443/1999 : X-ray spectral analysis of AGNs (Brightman+, 2014)
J/ApJ/788/159 : 17 Seyfert 1 galaxies light curves (Koshida+, 2014)
J/A+A/563/A57 : Long-term variability of AGN at hard X-rays (Soldi+, 2014)
J/A+A/579/A115 : SUDARE-VOICE variability-selection of AGN (Falocco+, 2015)
J/ApJ/802/89 : Luminosity function of X-ray-selected AGNs (Buchner+, 2015)
J/ApJ/815/L13 : Compton-thick AGNs from Swift/BAT 70-months (Ricci+, 2015)
J/A+A/588/A70 : Hard X-ray view of the soft excess in AGN (Boissay+, 2016)
J/ApJS/224/15 : Improved 2Ms and 250ks Chandra catalogs (Xue+, 2016)
J/ApJ/831/145 : 6Ms Chandra long-term analyses of AGNs (Yang+, 2016)
J/MNRAS/471/364 : Spectral curvature values for AGNs (Baronchelli+, 2017)
J/ApJS/228/2 : Chandra Deep Field-South survey: 7Ms sources (Luo+, 2017)
J/ApJS/232/8 : AGNs X-ray spectral analyses from 7Ms CDF-S (Liu+, 2017)
J/ApJS/236/48 : The Chandra UDS survey (X-UDS) (Kocevski+, 2018)
J/ApJ/869/171 : Chandra observations of NuSTAR sources (Tomsick+, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Field CDF North or South
6- 9 I4 --- XID [4/1004] Identifier, 2Ms CDF-N catalog
or 7Ms CDF-S catalog (1)
11- 21 F11.7 deg RAdeg [52.91/189.71] Right ascension of X-ray
source (J2000)
23- 33 F11.7 deg DEdeg [-28/62.45] Declination of X-ray
source (J2000)
35- 39 F5.3 --- zFINAL [0.18/5.4] Final redshift adopted (2)
41- 45 A5 --- f_zFINAL Redshift type; "ZSPEC" (191 occurrences)
or "ZPHOT"
47- 50 F4.2 --- Gamma [1.4/2.6] Photon index
52- 56 F5.2 --- e_Gamma [1.4/2.4]?=-1 1 sigma lower limit
value of Gamma
58- 62 F5.2 --- E_Gamma [1.4/2.6]?=-1 1 sigma upper limit
value of Gamma
64- 64 A1 --- f_Gamma Flag of whether photon index is fixed
66- 69 F4.2 10+24/cm2 NH [0.1/8.6] Hydrogen column density
71- 75 F5.2 10+24/cm2 e_NH [0.01/6.3]?=-1 1 sigma lower limit
value of NH
77- 81 F5.2 10+24/cm2 E_NH [0.1/8]?=-1 1 sigma upper limit
value of NH
83- 87 F5.2 [10-7W] logL [42/45.3] log of 2-10keV absorption
corrected luminosity (in erg/s)
89- 92 I4 ct Cts [20/4191] 0.5-7keV net counts
94- 98 F5.2 --- HR [-0.6/0.93]?=-9.99 Hardness ratio (3)
100-100 A1 --- Model Best fit spectral fitting model (4)
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Note (1): Identifier in the 2Ms CDF-N catalog (Xue+ 2016, J/ApJS/224/15 --
<[XLB2016] CDFN NNN> in Simbad) or 7Ms CDF-S catalog
(Luo+ 2017, J/ApJS/228/2 -- <[LBX2017] NNNN> in Simbad)
Note (2): Final redshift adopted from the 2Ms CDF-N catalog
(Xue+ 2016, J/ApJS/224/15) or 7Ms CDF-S catalog (Luo+ 2017, J/ApJS/228/2)
Note (3): HR=(H-S)/(H+S), where H stands for the observed-frame 2-7keV count
rate and S stands for the 0.5-2keV count rate. See Section 4.3.
Note (4): Model definitions (see Section 3.2) as follows:
----------------------------
Model fref fexs
----------------------------
A 10^-8 0
B 10^-8 0<fexs<0.1
C 1.0 0
D 1.0 0<fexs<0.1
----------------------------
fref and fexs are, respectively, the reflection and the soft-excess
fraction
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Nov-2020