J/A+A/711/A285ivo://CDS.VizieR/J/A+A/711/A285CDSEuclid Coll.: Fu Y.Bouwens R.Caputi K.I.Vergani D.,Scialpi M.Margalef-Bentabol B.Wang L.Bolzonella M.Banerji M.,Banados E.Feltre A.Toba Y.Calhau J.Tarsitano F.Cunha P.A.C.,Humphrey A.Vietri G.Mannucci F.Bisogni S.Ricci F.Landt H.,Spinoglio L.Matamoro Zatarain T.Stern D.Page M.J.Alexander D.M.,Zamorani G.Roster W.Salvato M.Copin Y.Sorce J.G.Scott D.,Zhang Y.-H.Lusso E.Wolf J.Yang D.Rottgering H.J.A.Laloux B.,Siudek M.Belladitta S.Liu Q.Allevato V.Kuijken K.Andreon S.,Auricchio N.Baccigalupi C.Baldi M.Balestra A.Bardelli S.,Battaglia P.Biviano 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.,Costille A.Courbin F.Courtois H.M.Cropper M.Da Silva A.,Degaudenzi H.De Lucia G.Dolding C.Dole H.Dubath F.,Duncan C.A.J.Dupac X.Dusini S.Escoffier S.Fabricius M.,Farina M.Farinelli R.Ferriol S.Finelli F.Fosalba P.,Fourmanoit N.Frailis M.Franceschi E.Franzetti P.Fumana M.,Galeotta S.George K.Gillard W.Gillis B.Giocoli C.,Gracia-Carpio J.Grazian A.Grupp F.Guzzo L.Haugan S.V.H.,Hoekstra H.Holmes W.Hook I.M.Hormuth F.Hornstrup A.Jahnke K.,Jhabvala M.Joachimi B.Keihaenen E.Kermiche S.Kiessling A.,Kubik B.Kuemmel M.Kunz M.Kurki-Suonio H.Laureijs R.,Le Brun A.M.C.Ligori S.Lilje P.B.Lindholm V.Lloro I.,Mainetti G.Maino D.Maiorano E.Mansutti O.Marcin S.Marggraf O.,Markovic K.Martinelli M.Martinet N.Marulli F.Massey R.J.,Medinaceli E.Mei S.Melchior M.Mellier Y.Meneghetti M.Merlin E.,Meylan G.Mora A.Moresco M.Moscardini L.Nakajima R.Neissner C.,Nichol R.C.Niemi S.-M.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.Rossetti E.Saglia R.Sakr Z.Sapone D.,Sartoris B.Schirmer M.Schneider P.Schrabback T.Scodeggio M.,Secroun A.Sefusatti E.Seidel G.Serrano S.Simon P.Sirignano C.,Sirri G.Stanco L.Starck J.-L.Steinwagner J.Surace C.,Tallada-Crespi P.Tavagnacco D.Taylor A.N.Teplitz H.I.Tereno I.,Tessore N.Toft S.Toledo-Moreo R.Torradeflot F.Tutusaus I.,Valenziano L.Valiviita J.Vassallo T.Veropalumbo A.Vibert D.,Wang Y.Weller J.Zacchei A.Zucca E.Ballardini M.Bozzo E.,Burigana C.Cabanac R.Calabrese M.Cappi A.Di Ferdinando D.,Escartin Vigo J.A.Gabarra L.Hartley W.G.Huertas-Company M.,Martin-Fleitas J.Matthew S.Mauri N.Metcalf R.B.Nucita A.A.,Pezzotta A.Poentinen M.Porciani C.Risso I.Scottez V.Sereno M.,Tenti M.Viel M.Wiesmann M.Akrami Y.Alvi S.Andika I.T.,Anselmi S.Archidiacono M.Atrio-Barandela F.Aubourg E.Bertacca D.,Bethermin M.Bisigello L.Blanchard A.Blot L.Bonici M.Borgani S.,Brown M.L.Bruton S.Calabro A.Camacho Quevedo B.Caro F.,Carvalho C.S.Castro T.Cogato F.Conseil S.Cooray A.R.,Cucciati O.Daste G.De Paolis F.Desprez G.Diaz-Sanchez A.,Diaz J.J.Di Domizio S.Diego J.M.Dimauro P.Duc P.-A.,Elkhashab M.Y.Enia A.Fang Y.Ferrari A.G.Finoguenov A.,Fontanot F.Franco A.Ganga K.Garcia-Bellido J.Gasparetto T.,Gautard V.Gaztanaga E.Giacomini F.Gianotti F.Gozaliasl G.,Gray M.Guidi M.Gutierrez C.M.Hall A.Hernandez-Monteagudo C.,Hildebrandt H.Hjorth J.Kajava J.J.E.Kang Y.Kansal V.,Karagiannis D.Kiiveri K.Kim J.Kirkpatrick C.C.Kruk S.,Le Brun V.Le Graet J.Legrand L.Lembo M.Lepori F.Leroy G.,Lesci G.F.Lesgourgues J.Liaudat T.I.Loureiro A.Macias-Perez J.,Magliocchetti M.Mancini C.Maoli R.Martins C.J.A.P.Maurin L.,Miluzio M.Monaco P.Moretti C.Morgante G.Nadathur S.Naidoo K.,Natoli P.Navarro-Alsina A.Nesseris S.Paoletti D.Passalacqua F.,Paterson K.Patrizii L.Pisani A.Potter D.Quai S.Radovich M.,Rocci P.-F.Rodighiero G.Sacquegna S.Sahlen M.Sanders D.B.,Sarpa E.Scarlata C.Schneider A.Sciotti D.Sellentin E.Shankar F.,Smith L.C.Soubrie E.Tanidis K.Tao C.Testera G.Teyssier R.,Tosi S.Troja A.Tucci M.Valieri C.Venhola A.Verza G.,Vielzeuf P.Viitanen A.Walton N.A.Weaver J.R.2026-07-23T07:32:53Z2026-07-23T07:46:50ZCDS support team

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

cds-question@unistra.frquasarsactive-galactic-nucleiinfrared-astronomyspectroscopyinfrared-photometryvisible-astronomyThe slitless spectroscopy mode of the Near-Infrared Spectrometer and Photometer (NISP) on board the Euclid telescope has enabled efficient spectroscopy of objects within a large field of view. Nevertheless, the relatively low spectral resolution, overlapping spectra, and contamination pose challenges to source classification and redshift determination using the NISP spectra alone. In this work, we present a large and homogeneous sample of bright quasars identified from the Euclid Quick Data Release (Q1), constructed by combining high-purity candidate selections from Gaia and WISE with the new spectroscopic capabilities of Euclid. Through visual inspection of the Euclid spectra of these quasar candidates, we identify approximately 3500 quasars and determine reliable redshifts in the range of 0<z<4.8. Of these, 2686 are new spectroscopic identifications relative to existing public compilations. We generated the first Euclid composite spectrum of quasars covering rest-frame near- ultraviolet (NUV) to near-infrared (NIR) wavelengths without telluric lines, which will be pivotal to NIR quasar spectral analysis. We obtained an empirical spectroscopic depth of JE 21.5 and HE 21.3 at the sensitivity of the Wide Field Survey, beyond which the number of securely identified quasars declines sharply. Accordingly, the sample presented in this paper comprises spectroscopically confirmed quasars brighter than these limits. We analysed morphological parameters from the Visible Camera (VIS) using Sersic and model-independent (CAS) metrics, and a deep-learning point spread function fraction to track nuclear dominance. The VIS morphologies show a clear redshift dependence: at low redshift (z<0.5), obvious host structures are common and a single Sersic model fits about half of the sources; at intermediate redshift (0.5<z<2), the nuclear component dominates, with 90% of the Sersic fits saturating at the upper index limit. In this intermediate redshift regime, fPSF is available, and we use it as a more reliable compactness measure than the single-Sersic and CAS parameters to quantify nuclear versus host emission. We also explore the novel Euclid NIR colour space and discuss the role of these quasars in refining active galactic nucleus selection techniques for future Euclid data releases.2026A&A...711A.285Ehttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/711/A285CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/388 : Euclid final merged catalog. Q1 data release (Euclid Coll., 2025)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/711/A285https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/711/A285http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/711/A285https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/711/A285https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/711/A285http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/711/A285GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/711/A285/tableb1 (Catalogue of spectroscopically identified bright quasars from Euclid Q1)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/711/A285/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/711/A285/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/711/A285/tableb1?GETtext/xml+votable180.050000true67.06712-48.078158890.0055555555555555564/2145 5/2557 2559 2901 2903 3839 4010-4011 8506 8579 8592 8983 8989 9032 6/10235 11601 11603 11609 15353-15355 16034-16035 16038 16056 33979 33982-33983 34028-34030 34307 34309-34311 34313-34315 34337 34339-34342 34352-34353 34372 34374 34376-34377 35926-35927 35929-35931 35953 35955 35964 36104 36106-36107https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/711/A285?format=asciiOpticalInfrareddefaultJ/A+A/711/A285/table2Mean, geometric mean, and median Euclid Q1 quasar composite spectra, along with RMS, S/N and the number of spectra in each wavelength binrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambda[240.0/1700.0] Wavelength bin center (nm)nmem.wldoubleFluxMean[0.77/16.58] Arithmetic-mean flux density (arbitrary units)phot.fluxdoublee_FluxMean[0.0/1.23] Uncertainty on arithmetic-mean flux densitystat.errordoubleFluxGeo[0.72/15.98] Geometric-mean flux density (arbitrary units)phot.fluxdoublee_FluxGeo[0.0/12.31] Uncertainty on geometric-mean flux densitystat.errordoubleFluxMed[0.79/17.12] Median flux density (arbitrary units)phot.fluxdoubleFluxRMS[0.04/5.09] RMS flux density in bin (arbitrary units)stat.errordoublesnr[9.68/616.47] Signal-to-noise ratio in binstat.snrdoublenSpectra[5/1761] Number of spectra contributing to the binmeta.numberintJ/A+A/711/A285/tableb1Catalogue of spectroscopically identified bright quasars from Euclid Q1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObjectIdEuclid Q1 unique source identifier (object_id)meta.idNameIAU-formatted source name (EUCL JHHMMSS.ss+DDMMSS.s) (name)meta.id;meta.maincharRAJ2000Source barycenter right ascension (J2000) (ra)degpos.eq.ra;meta.mainDEJ2000Source barycenter declination (J2000) (dec)degpos.eq.dec;meta.mainClassviVisual classification of the source (class_vi)meta.code.classcharzviVisual redshift of the source (z_vi)src.redshift.photdoublesumMaskSum of the mask values of the spectrum within [12047, 18734]{AA} (sum_mask)meta.numberNinvalidNumber of invalid pixels in the spectrum within [12047, 18734]{AA} (n_invalid)meta.numbermedSNRMedian signal-to-noise ratio of the spectrum within [12047, 18734]{AA} (med_snr)stat.snrdoublemumax-magThe difference between mu_max and mag_stargal_sep, valid even for NIR-only sources (sec-2 mumax_minus_)mag.arcsec**-2stat.fit.paramdoubleKronRadiusMajor semi-axis (in pixels) of the elliptical aperture used for total (Kron) aperture photometry on the detection image (kron_radius)pixphys.angSize;srcdoubleGaiaDR3? Associated Gaia source id (gaia_id)meta.idnullablefpsf? PSF fraction of the source from VIS image (f_psf) (1)stat.fit.paramdoublenullableVISmagpsf? VIS IE band PSF-fitting AB magnitude (from flux_vis_psf) (mag_vis_psf)magphot.mag;em.optdoublenullablee_VISmagpsf? Error on VIS IE band PSF- fitting AB magnitude (magerr_vis_psf)magstat.errordoublenullableYEmag? YE band template-fit AB magnitude (from flux_y_templfit) (mag_y_templfit)magphot.mag;em.IR.Jdoublenullablee_YEmag? Error on YE band template- fit AB magnitude (magerr_y_templfit)magstat.error;phot.magdoublenullableJEmag? JE band template-fit AB magnitude (from flux_j_templfit) (mag_j_templfit)magphot.mag;em.IR.Jdoublenullablee_JEmag? Error on JE band template- fit AB magnitude (magerr_j_templfit)magstat.error;phot.magdoublenullableHEmag? HE band template-fit AB magnitude (from flux_h_templfit) (mag_h_templfit)magphot.mag;em.IR.Hdoublenullablee_HEmag? Error on HE band template- fit AB magnitude (magerr_h_templfit)magstat.error;phot.magdoublenullable