J/A+A/697/A123ivo://CDS.VizieR/J/A+A/697/A123doi:10.26093/cds/vizier.36970123CDSPouliasis 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.2025-06-02T20:01:22Z2025-05-15T08:53:32ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fractive-galactic-nucleiredshiftedx-ray-sourcesX-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 (1240deg^2^), alongside the extensive optical Dark Energy Survey (DES, 5000deg^2^) 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 185deg^2^. 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 {eta}<=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 (logN_H_[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.2025A&A...697A.123Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/697/A123CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIX/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)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/697/A123https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/697/A123http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/697/A123https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/697/A123https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/697/A123http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/697/A123GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/697/A123/table (Final high-z X-ray-selected AGN)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/697/A123/table?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/697/A123/table?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/697/A123/table?GETtext/xml+votable180.050000true35.92330696712-4.209323956770.0055555555555555565/4421-4423 4425 4457 11542 11544-11545 6/16510 16666 16701-16702 16712-16714 17497 17509-17510 17516 17518 17525 17529 17533 17622-17623 17662 17667 17670-17671 17674-17675 17677-17679 17681-17683 17696-17697 17699 17704 17708 17712-17714 17716 17727 17730 17749 17754 17761-17762 17766-17767 17771 17773 17777 17797 17812 17814 17818 17827 17833 17835-17836 17840 17856 17955 17980 18006 18009-18013 18018 18020 18022 18032 18034 18062 18069 18071 18084-18085 18091-18092 18096 18099 18112 18747 18779 18784-18786 18789-18791 18794 18796 18800 18823 18858 18862 18867 19021 19027 19033-19034 19036 19042 19045 19053 19085 19087 19091 19095 19099 20489 20494 20507 20510 20516 20520 20537 20624 21016 21033 21133 21154 21169-21171 33193 33209 33241 33243 33260-33261 33265 33276 33471 33502 33513 33549 33558 33576 33586 33608 33614 33619 33628 33635 33644 33649 33651 33662 33668 33692 33702 33712-33713 33717 33769 33783 33866 33878-33879 33894 33921 33944 33948 33950 33954-33955 33960 33980 33984 34000-34002 34023 34034-34035 34038 34054 34071 34074 34088 34095 34104 34139 34160 34186 34229 34238 34258 34260 34265 34271-34273 34290 34294-34295 34297 34315 34324 34334 34356 34368 34382 34403 34412 34423 34430 34443 34471 34480 34493-34494 34496 34531 34533-34535 34541 34653 34655 34672 34674 34715 34739 34805 34845 34847 34881 34905 34930 34975 34992 35045 35053 35055 35071 35078 35082 35097 35100 35147 35161 35180 35240 35256 35272 35343 35361 35365 35382-35383 35387-35390 35429 35473 35476 35536 35864 35933-35935 35957 36082 36104 36106 36144 36172-36173 36231 36234 36290 36308 36431 36621 36626 36632 36678 36713 36771 36774-36775 36777 36781 36784-36785 36792 36795 36798 36800 45485 45497 45536-45537 45543 45686 45692 45814-45815 45854 45860 45873 45887 45893 45897 45942 45948 45957-45958 45962 45970 45981 45984 45986 46017 46019 46022 46024 46034 46036 46046 46101 46105 46108 46151 46153 46155-46158 46162-46164 46166-46167 46172-46174 46188 46192 46194 46196 46237 46345 46362-46363 46395 46399 46424 46440 46474 46477 46484 46632 46726 46732 46737-46740 46750 46762 47463https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/697/A123?format=asciiX-raydefaultJ/A+A/697/A123/tableFinal high-z X-ray-selected AGNRAJ2000Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainFluxX-ray flux in 0.2-12keV bandmW.m**-2phot.flux;em.X-raydoublee_FluxError on X-ray fluxmW.m**-2stat.error;phot.fluxdoubleDESDES counterpart ID (Cat. II/371)meta.idVHS? VHS counterpart ID (Cat. II/367)meta.idnullableAllWISE? AllWISE counterpart ID (Cat. II/328)meta.idnullablezRedshiftsrc.redshiftfloatf_z[0/1] Redshift flag (0=phot, 1=spec)meta.codeintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordint4XMM4XMM-DR11 source identifiermeta.id;meta.main