Euclid Quick Data Release (Q1). Optical and near-infrared identification and classification of point-like X-ray selected sources
Abstract
To better understand the role of active galactic nuclei (AGN) in galaxy evolution, it is crucial to achieve a complete and pure AGN census. 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 identifyed, classifyed, and determined the redshifts of 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), we identify the CTPs to 11 286 X-ray sources from the three X-ray telescopes. For the large majority of 10 194 sources, the associations are unique, with the remaining 10% of multi-CTP cases equally split between XMM-Newton and eROSITA. ML is then used to distinguish between Galactic (8%) and extragalactic (92%) sources. We computed photo-zs using deep learning for the 8617 sources detected in the 10th data release of the DESI Legacy Survey, reaching an accuracy and a fraction of outliers of about 5%. Based on their X-ray luminosities, over 99% of CTPs identified as extragalactic are classified as AGN, most of which appear unobscured given their hardness ratios. With this paper, we release our catalogue, which includes identifiers, basic X-ray properties, the details of the associations, and additional features 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.
Keywords
Cite
@article{arxiv.2503.15316,
title = {Euclid Quick Data Release (Q1). Optical and near-infrared identification and classification of point-like X-ray selected sources},
author = {Euclid Collaboration and W. Roster and M. Salvato and J. Buchner and R. Shirley and E. Lusso and H. Landt and G. Zamorani and M. Siudek and B. Laloux and T. Matamoro Zatarain and F. Ricci and S. Fotopoulou and A. Ferré-Mateu and X. Lopez Lopez and N. Aghanim and B. Altieri and A. Amara and S. Andreon and N. Auricchio and H. Aussel and C. Baccigalupi and M. Baldi and A. Balestra and S. Bardelli and P. Battaglia and A. Biviano and A. Bonchi and E. Branchini and M. Brescia and J. Brinchmann and S. Camera and G. Cañas-Herrera and V. Capobianco and C. Carbone and J. Carretero and S. Casas and M. Castellano and G. Castignani and S. Cavuoti and K. C. Chambers and A. Cimatti and C. Colodro-Conde and G. Congedo and C. J. Conselice and L. Conversi and Y. Copin and F. Courbin and H. M. Courtois and M. Cropper and A. Da Silva and H. Degaudenzi and G. De Lucia and A. M. Di Giorgio and C. Dolding and H. Dole and F. Dubath and C. A. J. Duncan and X. Dupac and S. Dusini and S. Escoffier and M. Fabricius and M. Farina and R. Farinelli and F. Faustini and S. Ferriol and F. Finelli and P. Fosalba and N. Fourmanoit and M. Frailis and E. Franceschi and S. Galeotta and K. George and B. Gillis and C. Giocoli and J. Gracia-Carpio and B. R. Granett and A. Grazian and F. Grupp and S. Gwyn and S. V. H. Haugan and W. Holmes and I. M. Hook and F. Hormuth and A. Hornstrup and P. Hudelot and K. Jahnke and M. Jhabvala and E. Keihänen and S. Kermiche and A. Kiessling and B. Kubik and M. Kümmel and M. Kunz and H. Kurki-Suonio and Q. Le Boulc'h and A. M. C. Le Brun and D. Le Mignant and S. Ligori and P. B. Lilje and V. Lindholm and I. Lloro and G. Mainetti and D. Maino and E. Maiorano and O. Mansutti and S. Marcin and O. Marggraf and M. Martinelli and N. Martinet and F. Marulli and R. Massey and D. C. Masters and E. Medinaceli and S. Mei and M. Melchior and Y. Mellier and M. Meneghetti and E. Merlin and G. Meylan and A. Mora and M. Moresco and L. Moscardini and R. Nakajima and C. Neissner and S. -M. Niemi and J. W. Nightingale and C. Padilla and S. Paltani and F. Pasian and K. Pedersen and W. J. Percival and V. Pettorino and S. Pires and G. Polenta and M. Poncet and L. A. Popa and L. Pozzetti and F. Raison and R. Rebolo and A. Renzi and J. Rhodes and G. Riccio and E. Romelli and M. Roncarelli and R. Saglia and Z. Sakr and A. G. Sánchez and D. Sapone and B. Sartoris and J. A. Schewtschenko and M. Schirmer and P. Schneider and T. Schrabback and A. Secroun and G. Seidel and M. Seiffert and S. Serrano and P. Simon and C. Sirignano and G. Sirri and L. Stanco and J. Steinwagner and P. Tallada-Crespí and D. Tavagnacco and A. N. Taylor and I. Tereno and S. Toft and R. Toledo-Moreo and F. Torradeflot and I. Tutusaus and L. Valenziano and J. Valiviita and T. Vassallo and G. Verdoes Kleijn and A. Veropalumbo and Y. Wang and J. Weller and A. Zacchei and F. M. Zerbi and I. A. Zinchenko and E. Zucca and V. Allevato and M. Ballardini and M. Bolzonella and E. Bozzo and C. Burigana and R. Cabanac and A. Cappi and D. Di Ferdinando and J. A. Escartin Vigo and L. Gabarra and M. Huertas-Company and J. Martín-Fleitas and S. Matthew and N. Mauri and R. B. Metcalf and A. Pezzotta and M. Pöntinen and C. Porciani and I. Risso and V. Scottez and M. Sereno and M. Tenti and M. Viel and M. Wiesmann and Y. Akrami and I. T. Andika and S. Anselmi and M. Archidiacono and F. Atrio-Barandela and C. Benoist and K. Benson and D. Bertacca and M. Bethermin and L. Bisigello and A. Blanchard and L. Blot and H. Böhringer and M. L. Brown and S. Bruton and A. Calabro and F. Caro and C. S. Carvalho and T. Castro and F. Cogato and A. R. Cooray and O. Cucciati and S. Davini and F. De Paolis and G. Desprez and A. Díaz-Sánchez and J. J. Diaz and S. Di Domizio and J. M. Diego and A. Enia and Y. Fang and A. G. Ferrari and A. Finoguenov and A. Fontana and A. Franco and K. Ganga and J. García-Bellido and T. Gasparetto and V. Gautard and E. Gaztanaga and F. Giacomini and F. Gianotti and G. Gozaliasl and M. Guidi and C. M. Gutierrez and A. Hall and W. G. Hartley and S. Hemmati and C. Hernández-Monteagudo and H. Hildebrandt and J. Hjorth and J. J. E. Kajava and Y. Kang and V. Kansal and D. Karagiannis and K. Kiiveri and C. C. Kirkpatrick and S. Kruk and J. Le Graet and L. Legrand and M. Lembo and F. Lepori and G. Leroy and G. F. Lesci and J. Lesgourgues and L. Leuzzi and T. I. Liaudat and A. Loureiro and J. Macias-Perez and G. Maggio and M. Magliocchetti and F. Mannucci and R. Maoli and C. J. A. P. Martins and L. Maurin and M. Miluzio and P. Monaco and C. Moretti and G. Morgante and K. Naidoo and A. Navarro-Alsina and S. Nesseris and F. Passalacqua and K. Paterson and L. Patrizii and A. Pisani and D. Potter and S. Quai and M. Radovich and S. Sacquegna and M. Sahlén and D. B. Sanders and E. Sarpa and A. Schneider and D. Sciotti and E. Sellentin and F. Shankar and L. C. Smith and K. Tanidis and G. Testera and R. Teyssier and S. Tosi and A. Troja and M. Tucci and C. Valieri and A. Venhola and D. Vergani and G. Verza and P. Vielzeuf and A. Viitanen and N. A. Walton and E. Soubrie and D. Scott},
journal= {arXiv preprint arXiv:2503.15316},
year = {2025}
}
Comments
Paper accepted as part of the A&A Special Issue `Euclid Quick Data Release (Q1)', 24 pages, 22 figures. PICZL code (Roster et al. 2024) used for computing the photo-z, is also released