J/A+A/711/A16ivo://CDS.VizieR/J/A+A/711/A16CDSEuclid Collaboration: Roster W.Salvato M.Buchner J.Shirley R.,Lusso E.Landt H.Zamorani G.Siudek M.Laloux B.Matamoro Zatarain T.,Ricci F.Fotopoulou S.Ferre-Mateu A.Lopez Lopez X.Aghanim N.,Altieri B.Amara A.Andreon S.Auricchio N.Aussel H.Baccigalupi C.,Baldi M.Balestra A.Bardelli S.Battaglia P.Biviano A.Bonchi A.,Branchini E.Brescia M.Brinchmann J.Camera S.Canas-Herrera G.,Capobianco V.Carbone C.Carretero J.Casas S.Castellano M.,Castignani G.Cavuoti S.Chambers K.C.Cimatti A.Colodro-Conde C.,Congedo G.Conselice C.J.Conversi L.Copin Y.Courbin F.,Courtois H.M.Cropper M.Da Silva A.Degaudenzi H.De Lucia G.,Di Giorgio A.M.Dolding C.Dole H.Dubath F.Duncan C.A.J.Dupac X.,Dusini S.Escoffier S.Fabricius M.Farina M.Farinelli R.Faustini F.,Ferriol S.Finelli F.Fosalba P.Fourmanoit N.Frailis M.,Franceschi E.Galeotta S.George K.Gillis B.Giocoli C.,Gracia-Carpio J.Granett B.R.Grazian A.Grupp F.Gwyn S.,Haugan S.V.H.Holmes W.Hook I.M.Hormuth F.Hornstrup A.Hudelot P.,Jahnke K.Jhabvala M.Keihaenen E.Kermiche S.Kiessling A.Kubik B.,Kuemmel M.Kunz M.Kurki-Suonio H.Le Boulc'h Q.Le Brun A.M.C.,Le Mignant D.Ligori S.Lilje P.B.Lindholm V.Lloro I.Mainetti G.,Maino D.Maiorano E.Mansutti O.Marcin S.Marggraf O.Martinelli M.,Martinet N.Marulli F.Massey R.Masters D.C.Medinaceli E.Mei S.,Melchior M.Mellier Y.Meneghetti M.Merlin E.Meylan G.Mora A.,Moresco M.Moscardini L.Nakajima R.Neissner C.Niemi S.-M.,Nightingale J.W.Padilla C.Paltani S.Pasian F.Pedersen K.,Percival W.J.Pettorino V.Pires S.Polenta G.Poncet M.Popa L.A.,Pozzetti L.Raison F.Rebolo R.Renzi A.Rhodes J.Riccio G.,Romelli E.Roncarelli M.Saglia R.Sakr Z.Sanchez A.G.Sapone D.,Sartoris B.Schewtschenko J.A.Schirmer M.Schneider P.Schrabback T.,Secroun A.Seidel G.Seiffert M.Serrano S.Simon P.Sirignano C.,Sirri G.Stanco L.Steinwagner J.Tallada-Crespi P.Tavagnacco D.,Taylor A.N.Tereno I.Toft S.Toledo-Moreo R.Torradeflot F.,Tutusaus I.Valenziano L.Valiviita J.Vassallo T.Verdoes Kleijn G.,Veropalumbo A.Wang Y.Weller J.Zacchei A.Zerbi F.M.Zinchenko I.A.,Zucca E.Allevato V.Ballardini M.Bolzonella M.Bozzo E.Burigana C.,Cabanac R.Cappi A.Di Ferdinando D.Escartin Vigo J.A.Gabarra L.,Huertas-Company M.Martin-Fleitas J.Matthew S.Mauri N.Metcalf R.B.,Pezzotta A.Poentinen M.Porciani C.Risso I.Scottez V.Sereno M.,Tenti M.Viel M.Wiesmann M.Akrami Y.Andika I.T.Anselmi S.,Archidiacono M.Atrio-Barandela F.Benoist C.Benson K.Bertacca D.,Bethermin M.Bisigello L.Blanchard A.Blot L.Boehringer H.,Brown M.L.Bruton S.Calabro A.Caro F.Carvalho C.S.Castro T.,Cogato F.Cooray A.R.Cucciati O.Davini S.De Paolis F.Desprez G.,Diaz-Sanchez A.Diaz J.J.Di Domizio S.Diego J.M.Enia A.Fang Y.,Ferrari A.G.Finoguenov A.Fontana A.Franco A.Ganga K.,Garcia-Bellido J.Gasparetto T.Gautard V.Gaztanaga E.Giacomini F.,Gianotti F.Gozaliasl G.Guidi M.Gutierrez C.M.Hall A.Hartley W.G.,Hemmati S.Hernandez-Monteagudo C.Hildebrandt H.Hjorth J.,Kajava J.J.E.Kang Y.Kansal V.Karagiannis D.Kiiveri K.,Kirkpatrick C.C.Kruk S.Le Graet J.Legrand L.Lembo M.Lepori F.,Leroy G.Lesci G.F.Lesgourgues J.Leuzzi L.Liaudat T.I.Loureiro A.,Macias-Perez J.Maggio G.Magliocchetti M.Mannucci F.Maoli R.,Martins C.J.A.P.Maurin L.Miluzio M.Monaco P.Moretti C.Morgante G.,Naidoo K.Navarro-Alsina A.Nesseris S.Passalacqua F.Paterson K.,Patrizii L.Pisani A.Potter D.Quai S.Radovich M.Sacquegna S.,Sahlen M.Sanders D.B.Sarpa E.Schneider A.2026-06-30T15:25:59Z2026-06-30T16:25:27ZCDS support team

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

cds-question@unistra.frsurveysx-ray-sourcesvisible-astronomyinfrared-astronomyTo better understand the role of active galactic nuclei (AGN) in galaxy evolution, it is crucial to work with a complete and pure AGN sample. X-ray surveys are key to this, but identifying their counterparts (CTPs) at other wavelengths remains challenging due to their larger positional uncertainties and limited availability of deeper, uniform ancillary data. Euclid is revolutionising this effort, offering extensive coverage of nearly the entire extragalactic sky, particularly in the near-infrared bands, where AGN are more easily detected. With the first Euclid Quick Data Release (Q1), we validated methods for identifying and classifying Euclid CTPs to known point-like sources from major X-ray surveys, including XMM- Newton, Chandra, and eROSITA. Using Bayesian statistics, combined with machine learning (ML), as incorporated in the algorithm NWAY, we identify the CTPs to 11286 X-ray sources from the three X-ray telescopes. For the large majority of 10194 sources, the association is unique, with the remaining ~10% of multi-CTP cases equally split between XMM-Newton and eROSITA. Six per cent of the Euclid CTPs are detected in more than one X-ray survey. ML is then used to distinguish between Galactic (8%) and extragalactic (92%) sources. We computed photo-zs using deep learning for the 9259 sources detected in the 10th data release of the DESI Legacy Survey, reaching an accuracy and a fraction of outliers of roughly 5%. Based on their X-ray luminosities, all CTPs identified as extragalactic are classified as AGN, most of which appear as type I AGN according to their hardness ratios. With this paper, we release our catalogue, which includes identifiers, basic X-ray properties, the reliability of the associations, and additional property extensions such as Galactic/extragalactic classifications and photometric/spectroscopic redshifts. We also provide probabilities for sub-selecting the sample based on purity and completeness, allowing users to tailor the sample according to their specific needs.2026A&A...711A..16Ehttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/711/A16CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/388 : Euclid final merged catalog. Q1 data releaseIX/68 : XMM-Newton Serendipitous Source Catalogue 4XMM-DR12IX/70 : Chandra Source Catalog Release 2 (CSC 2.1) (Evans+, 2024)J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)J/A+A/711/A10 : Euclid (Q1). Census of dwarf galaxies (Euclid Coll., 2026)J/A+A/711/A16 : X-ray point-like sources of Euclid (Q1) (Euclid Coll.+, 2026)J/A+A/711/A37 : Ultracool dwarfs in Euclid Deep Fields (Zerjal+, 2026)J/A+A/711/A38 : Euclid Q1. Photometric studies of known transientsJ/A+A/711/A39 : Euclid Q1. Secondary nuclei in ET galaxies (Fabricius+, 2026)J/A+A/711/A20 : Galaxies of Euclid (Q1) (Euclid Coll.+, 2026)J/A+A/711/A24 : Euclid Q1. Little red dots properties (Euclid Coll., 2026)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/711/A16https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/711/A16http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/711/A16https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/711/A16https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/711/A16http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/711/A16GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/711/A16/catalog (Xray-EUCLID released CTP catalogue)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/711/A16/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/711/A16/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/711/A16/catalog?GETtext/xml+votable180.050000true52.05016522484401-27.3880282215150040.0055555555555555564/2145 5/2901 8506-8507 8579 8585 8592 8982-8983 8989 9032 6/10230 10236 10238-10239 11603 11609 11613 15359 16034 16042-16043 16046 33979 33981-33983 34307 34309-34311 34313 34315 34336-34337 34339 34352-34353 34372 34374 34376-34377 35926-35927 35953 35955 35964 36098 36104 36106-36107https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/711/A16?format=asciiX-rayOpticalInfrareddefaultJ/A+A/711/A16/catalogXray-EUCLID released CTP cataloguerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordinteposPositional uncertainty of X-ray source (Xray_pos_err)arcsecstat.error;posdoubleFX? The mean flux (0.5-2.3keV) of all the detections of the X-ray source (Fx)mW.m**-2phot.flux;em.X-raydoublenullablezsp? Spectroscopic redshift (z_spec)src.redshiftdoublenullablee_zsp[]? Error on the spec-z (z_err)stat.errordoublenullableCatspecParent catalog of spec-z match (Cat_spec)meta.id;meta.datasetcharzph? PICZL photometric redshift (phz) (3)src.redshift.photdoublenullablee_zph? Photo-z lower 1 sigma error (phz_1sl)stat.errordoublenullableE_zph? Photo-z upper 1 sigma error (phz_1su)stat.error;stat.maxfloatnullableXray-EUCLIDConcatenation of X-ray_ID and EUCLID_ID (unique) (Xray_EUCLID_ID)meta.idcharXrayX-ray source identifier (unique) (Xray_ID)meta.id;meta.maincharRAJ2000J2000 Right Ascension of the X-ray source in the parent catalog (Xray_RA)degpos.eq.ra;meta.mainindexedDEJ2000J2000 Declination of the X-ray source in the parent catalog (Xray_DEC)degpos.eq.dec;meta.mainindexede_FX? Error on the mean flux (0.5-2.3keV) of all the detections of the (EFx)mW.m**-2stat.errordoublenullableSNX? Signal to noise ratio for FX/e_FX (S_Nx)stat.snrdoublenullableHR? Hardness ratio considering soft 0.5-2.0keV and hard (4XMM DR14: 2. (HR)phot.flux;em.X-ray.soft;arith.ratiodoublenullableEUCLIDEUCLID source identifier (unique) (EUCLID_ID)meta.idRAEdegJ2000 Right Ascension of the counterpart in Euclid catalog (EUCLID_RA)degpos.eq.raDEEdegJ2000 Declination of the counterpart in Euclid catalog (EUCLID_DEC)degpos.eq.decEeposPositional uncertainty of Euclid source (EUCLID_pos_err)arcsecstat.error;posfloatEPXrayProbability to be an X-ray emitter based on the Random Forest model (EUCLID_P_Xray)stat.fit.goodnessdoubleEPGalProbability of being a Galactic rather than extragalactic source bas (EUCLID_P_Gal)stat.fit.goodnessdoubleSepEXDistance between Euclid and X-ray source (Separation_EUCLID_Xray)arcsecpos.angDistancedoublelogDistbfLogarithm of ratio between prior and posterior, from separation, positional error, and number density (dist_bayesfactor) (2)stat.fit.paramdoublepdistpostDistance posterior probability comparing this association vs. no association (dist_post) (2)stat.fit.paramdoublebiasprobaProbability weighting introduced by the Euclid-based prior. 1 indicates no change) (bias_EUCLID_Xray_proba)stat.fit.goodnessdoublepsingleDistance posterior probability comparing this association vs. no as weighted by the prior (p_single) (2)stat.fit.goodnessdoubleEDFEuclid deep field (EDF)obs.fieldcharpanyFor each entry in the X-ray catalogue, the probability that there is a counterpart in LS10 for each X-ray entry (p_any) (2)stat.fit.goodnessdoublepiRelative probability of the X-ray/Euclid match (p_i) (2)stat.fit.goodnessdoubleMatchFlag[1/2] 1 for the most probable match, if existing; 2: almost as good solutions (pi/pibest>0.5) (match_flag)meta.codeintRALdeg? Legacy survey DR10 J2000 Right Ascension of the CPT (LS10_RA)degpos.eq.ranullableDELdeg? Legacy survey DR10 J2000 Declination of the CPT (LS10_DEC)degpos.eq.decnullableRAsdeg? J2000 Right Ascension of the spec-z match to the Euclid CTP (ra_spec)degpos.eq.ranullableDEsdeg? J2000 Declination of the spec-z match to the Euclid CTP (dec_spec)degpos.eq.decnullablezphL17? Photometric redshift (see Luo et al. 2017ApJS..228....2L, Cat. J/ApJS/228/2) (phz_Luo17)src.redshift.photfloatnullablezfinal? zsp when available, otherwise zphL17 or zph (z_final)src.redshift;pos.heliocentricdoublenullableLX? Apparent rest-frame soft (0.5-2keV) Xray luminosity (Lx) (4)1e-07Wphys.luminosity;em.X-raydoublenullableXrayCatX-ray source catalogue (Xray_CAT) (1)meta.id;meta.datasetcharLS10Legacy survey DR10 unique identifier of the CPT by concatenation of RELEASE, BRICKID, and OBJID (LS10_FULLID)meta.idchar