J/A+A/697/A123 4XMM high-z AGN (Pouliasis+, 2025)
Identification of high-redshift X-ray active galactic nuclei in the 4XMM-DR11
serendipitous catalogue using DES data. Comparative analysis with optically
selected QSOs.
Pouliasis E., Ruiz A., Georgantopoulos I., Akylas A., Webb N.A.,
Carrera F.J., Mateos S., Nebot A., Watson M.G., Pineau F.X., Motch C.
<Astron. Astrophys. 697, A123 (2025)>
=2025A&A...697A.123P 2025A&A...697A.123P (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Redshifts ; X-ray sources
Keywords: methods: data analysis - galaxies: active - galaxies: high-redshift -
quasars: supermassive black holes - early Universe -
X-rays: galaxies
Abstract:
X-rays provide a robust method in identifying active galactic nuclei
(AGN). However, in the high-redshift Universe (z≥3.0), their space
density is relatively low and due to the small areas covered by X-ray
surveys, the selected AGN are poorly sampled. Deep optical and
infrared (IR) data are essential for locating counterparts and
determining redshifts. In this work, we leverage the XMM-Newton
4XMM-DR11 serendipitous catalogue (1240deg2), alongside the
extensive optical Dark Energy Survey (DES, 5000deg2) and the near-IR
VISTA Hemisphere Survey (VHS) to select one of the largest
high-redshift X-ray AGN samples to date. Our analysis is focussed on
the overlapping area of these surveys, covering about 185deg2. In
addition, we aspire to compare the properties of the X-ray AGN with
optically selected QSOs. For sources without spectroscopic data
(∼80%), we estimated the photometric redshifts using both spectral
energy distribution (SED) fitting and machine-learning algorithms.
Among the ∼65000 X-ray sources in the 4XMM-DES-VHS area, we ended up
with 833 z≥3.5 AGN (11% having spec-z information) with a high level
of reliability, along with a fraction of outliers of η≤10%. The
sample completeness is ∼90%, driven by the depth of DES data.
Only ∼10% of the X-ray selected AGN are also optical QSOs and vice
versa. Our findings indicate an observed absorbed fraction
(logNH[cm-2]≥23) of 20-40% for the X-ray AGN, significantly
higher than that of optical QSOs. X-ray AGN exhibit fainter observed
optical magnitudes and brighter mid-IR magnitudes than optical QSOs.
Their median rest-frame SED shapes differ notably with optical QSOs
being dominated by AGN emission in the UV-optical wavelengths. While
the median SEDs of X-ray AGN suggest extinction in the UV-optical
range, individual sources exhibit a wide range of spectral shapes,
indicating significant diversity within the population. This analysis
supports the notion that X-ray-selected and optically selected AGN
represent distinct and complementary populations.
Description:
In this work, we made use of the 4XMM-DR11 catalogue (1240deg2) that
contains all the serendipitous X-ray sources from the XMM-Newton space
telescope, in combination with the deep optical second release of the
Dark Energy Survey (DES-DR2, 5000deg2) to select the largest sample
so far of high-redshift (z≥3.5) X-ray selected AGN.
The table contains the sample of high-z 4XMM X-ray sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 125 833 Final high-z X-ray-selected AGN
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See also:
IX/65 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR11 (Webb+, 2022)
II/328 : AllWISE Data Release (Cutri+ 2013)
II/367 : The VISTA Hemisphere Survey (VHS) catalog DR5 (McMahon+, 2013)
II/371 : The Dark Energy Survey (DES): Data Release 2 (Abbott+, 2021)
Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 15 I15 --- 4XMM 4XMM-DR11 source identifier
17- 31 F15.11 deg RAdeg Right Ascension (J2000)
33- 47 F15.11 deg DEdeg Declination (J2000)
49- 60 E12.6 mW/m2 Flux X-ray flux in 0.2-12keV band
62- 73 E12.6 mW/m2 e_Flux Error on X-ray flux
75- 84 I10 --- DES DES counterpart ID (Cat. II/371)
86- 97 I12 --- VHS ? VHS counterpart ID (Cat. II/367)
99-117 I19 --- AllWISE ? AllWISE counterpart ID (Cat. II/328)
119-123 F5.3 --- z Redshift
125 I1 --- f_z [0/1] Redshift flag (0=phot, 1=spec)
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Acknowledgements:
Ektoras Pouliasis, ektoraspou(at)gmail.com
(End) Patricia Vannier [CDS] 06-May-2025