J/A+A/638/A45 Obscuration properties of red AGNs in XXL-N (Masoura+, 2020)
The XXL Survey. XL. Obscuration properties of red AGNs in XXL-N.
Masoura V.A., Georgantopoulos I., Mountrichas G., Vignali C.,
Koulouridis E., Chiappetti L., Fotopoulou S., Paltani S., Pierre M.
<Astron. Astrophys., 638, A45 (2020)>
=2020A&A...638A..45M 2020A&A...638A..45M (SIMBAD/NED BibCode)
ADC_Keywords: X-ray sources ; Active gal. nuclei
Keywords: galaxies: active - X-rays: galaxies
Abstract:
The combination of optical and mid-infrared (MIR) photometry has been
extensively used to select red active galactic nuclei (AGNs). Our aim
is to explore the obscuration properties of these red AGNs with both
X-ray spectroscopy and spectral energy distributions (SEDs). In this
study, we re-visit the relation between optical/MIR extinction and
X-ray absorption. We use IR selection criteria, specifically the W1
and W2 WISE bands, to identify 4798 AGNs in the XMM-XXL area
(∼25deg2). Application of optical/MIR colours (r-W2>6) reveals 561
red AGNs (14%). Of these, 47 have available X-ray spectra with at
least 50 net (background-subtracted) counts per detector. For these
sources, we construct SEDs from the optical to the MIR using the
CIGALE code. The SED fitting shows that 44 of these latter 47 sources
present clear signs of obscuration based on the AGN emission and the
estimated inclination angle. Fitting the SED also reveals ten systems
(∼20%) which are dominated by the galaxy. In these cases, the red
colours are attributed to the host galaxy rather than AGN absorption.
Excluding these ten systems from our sample and applying X-ray
spectral fitting analysis shows that up to 76% (28/37) of the IR red
AGNs present signs of X-ray absorption. Thus, there are nine sources
(∼20% of the sample) that although optically red, are not
substantially X-ray absorbed. Approximately 50% of these sources
present broad emission lines in their optical spectra. We suggest that
the reason for this apparent discrepancy is that the r-W2 criterion is
sensitive to smaller amounts of obscuration relative to the X-ray
spectroscopy. In conclusion, it appears that the majority of red AGNs
present considerable obscuration levels as shown by their SEDs. Their
X-ray absorption is moderate with a mean of NH∼1022cm-2.
Description:
We classify the 47 optically red AGNs of our sample as obscured or
unobscured using different criteria. Specifically, we examine their
X-ray spectra, SEDs, and optical spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 38 47 General properties of the red AGN sample
table3.dat 54 47 X-ray properties of the red AGN sample
table5.dat 32 47 SED properties of the red AGN sample
table6.dat 28 47 Optical properties of the red AGN sample
table7.dat 26 47 Comparison of the X-ray, SED, and optical
properties
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See also:
IX/49 : XXL Survey: First results (Pierre+, 2016)
IX/52 : XXL Survey. DR2 (Chiappetti+, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 19 A16 --- 3XLSS 3XLSS ID (JHHMMSS.s+DDMMSS)
21- 25 F5.3 --- z Redshift
26 A1 --- n_z [s/p] spectroscopic (s) or photometric (p)
redshift
28- 32 F5.2 mag rmag SDSS DR15 r magnitude (Vega)
34- 38 F5.2 mag W2mag W2 magnitude (Vega)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 19 A16 --- 3XLSS 3XLSS ID (JHHMMSS.s+DDMMSS)
20 A1 --- n_3XLSS [ib] Note on 3XLSS (1)
22 A1 --- l_NH Limit flag on NH
23- 27 F5.2 10+22cm-2 NH Hydrogen column density
29- 32 F4.1 10+22cm-2 NHG1.8 ? Hydrogen column density at GAMMA=1.8 (2)
34- 37 F4.2 --- GAMMA Photon index
39- 45 E7.2 [10-7W] logLX X-ray luminosity in 2-10keV band
47- 49 I3 --- C-stat C statistic
50 A1 --- --- [/]
51- 54 I4 --- dof Degree of freedom
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Note (1): Notes as follows:
b = Sources classified as X-ray obscured based on our strict criteria
(see text for more details)
i = Sources that satisfy the loosened X-ray criteria (see text)
Note (2): When GAMMA≤1.2, we quote the NH estimations with GAMMA fixed to
GAMMA=1.8.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 19 A16 --- 3XLSS 3XLSS ID (JHHMMSS.s+DDMMSS)
21- 22 I2 deg PSI Viewing angle of the torus (1)
24- 27 F4.2 --- fracAGN AGN fraction
29- 32 F4.2 --- chi2r Reduced chi2 value
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Note (1): We consider sources with PSI≤30° as Type 2 (edge-on),
40°≤PSI≤60° as intermediate and PSI≥70° as Type 1 AGNs,
based on their best-fit values.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 19 A16 --- 3XLSS 3XLSS ID (JHHMMSS.s+DDMMSS)
21- 28 A8 ---- Optical Optical properties (1)
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Note (1): Optically unobscured sources (Type 1) are considered to be those with
broad emission lines (BL). Whereas obscured sources (Type 2) exhibit only
narrow emission lines (NL) or a red continuum. The AGNs are characterised as
obscured, unobscured, or intermediate type (IMD) based on visual inspection of
their optical spectra. We note that in the optical spectra of
sources 13 and 22, while the MgII lines are broad, all other lines are narrow.
This is attributed to the wider area from which the MgII originates with
respect to the Balmer lines. These sources are characterized as IMD.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Sequential number
4- 19 A16 --- 3XLSS 3XLSS ID (JHHMMSS.s+DDMMSS)
20 A1 --- n_3XLSS [b/i] Note on 3XLSS (1)
22 I1 --- Xray [1/2] X-ray classification (2)
24 I1 --- SED [1/2] SED classification (2)
26 I1 --- Opt [0/3]? Optical-based classification (2)
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Note (1): Note as follows:
b = Sources classified as X-ray obscured based on our strict criteria
(see text for more details)
i = Sources that satisfy the loosened X-ray criteria (see text).
Note (2): Classification code as follows:
1 = unobscured, used to denote the classification of the sources based on
the various criteria
2 = obscured, used to denote the classification of the sources based on
the various criteria
0 = optical spectra that are too noisy to allow us to classify them
3 = optical spectra that are IMD type
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History:
From electronic version of the journal
References:
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(End) Patricia Vannier [CDS] 30-Sep-2020