June
2026
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2026A&A...711A..18E
Authors
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Euclid Collaboration
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Margalef-Bentabol, B.
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Wang, L.
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La Marca, A.
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Rodriguez-Gomez, V.
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Humphrey, A.
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Fotopoulou, S.
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Ricci, F.
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Toba, Y.
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Stevens, G.
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Mezcua, M.
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Roster, W.
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Knapen, J. H.
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Salvato, M.
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Siudek, M.
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Shankar, F.
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Matamoro Zatarain, T.
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Spinoglio, L.
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Dayal, P.
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Petley, J.
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Kondapally, R.
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Aghanim, N.
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Altieri, B.
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Amara, A.
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Andreon, S.
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Auricchio, N.
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Aussel, H.
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Baccigalupi, C.
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Baldi, M.
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Balestra, A.
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Bardelli, S.
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Battaglia, P.
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Biviano, A.
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Bonchi, A.
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Bonino, D.
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Branchini, E.
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Brescia, M.
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Brinchmann, J.
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Camera, S.
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Cañas-Herrera, G.
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Capobianco, V.
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Carbone, C.
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Carretero, J.
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Casas, S.
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Castellano, M.
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Castignani, G.
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Cavuoti, S.
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Chambers, K. C.
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Cimatti, A.
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Colodro-Conde, C.
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Congedo, G.
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Conselice, C. J.
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Conversi, L.
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Copin, Y.
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Costille, A.
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Courbin, F.
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Courtois, H. M.
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Cropper, M.
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Da Silva, A.
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Degaudenzi, H.
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De Lucia, G.
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Di Giorgio, A. M.
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Dolding, C.
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Dole, H.
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Dubath, F.
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Duncan, C. A. J.
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Dupac, X.
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Ealet, A.
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Escoffier, S.
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Farina, M.
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Farinelli, R.
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Faustini, F.
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Ferriol, S.
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Finelli, F.
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Frailis, M.
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Franceschi, E.
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Galeotta, S.
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George, K.
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Gillis, B.
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Giocoli, C.
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Gómez-Alvarez, P.
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Gracia-Carpio, J.
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Granett, B. R.
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Grazian, A.
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Grupp, F.
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Guzzo, L.
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Gwyn, S.
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Haugan, S. V. H.
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Holmes, W.
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Hook, I. M.
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Hormuth, F.
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Hornstrup, A.
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Hudelot, P.
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Jahnke, K.
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Jhabvala, M.
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Keihänen, E.
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Kermiche, S.
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Kiessling, A.
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Kubik, B.
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Kümmel, M.
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Kunz, M.
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Kurki-Suonio, H.
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Le Boulc'h, Q.
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Le Brun, A. M. C.
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Le Mignant, D.
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Liebing, P.
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Ligori, S.
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Lilje, P. B.
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Lindholm, V.
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Lloro, I.
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Mainetti, G.
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Maino, D.
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Maiorano, E.
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Mansutti, O.
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Marcin, S.
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Marggraf, O.
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Martinelli, M.
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Martinet, N.
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Marulli, F.
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Massey, R.
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Maurogordato, S.
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Medinaceli, E.
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Mei, S.
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Melchior, M.
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Mellier, Y.
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Meneghetti, M.
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Merlin, E.
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Meylan, G.
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Mora, A.
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Moresco, M.
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Moscardini, L.
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Nakajima, R.
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Neissner, C.
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Niemi, S.-M.
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Nightingale, J. W.
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Padilla, C.
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Paltani, S.
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Pasian, F.
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Pedersen, K.
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Percival, W. J.
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Pettorino, V.
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Pires, S.
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Polenta, G.
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Poncet, M.
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Popa, L. A.
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Pozzetti, L.
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Raison, F.
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Rebolo, R.
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Renzi, A.
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Rhodes, J.
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Riccio, G.
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Romelli, E.
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Roncarelli, M.
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Rottgering, H. J. A.
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Rusholme, B.
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Saglia, R.
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Sakr, Z.
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Sapone, D.
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Sartoris, B.
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Schewtschenko, J. A.
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Schneider, P.
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Schrabback, T.
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Secroun, A.
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Seidel, G.
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Seiffert, M.
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Serrano, S.
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Simon, P.
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Sirignano, C.
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Sirri, G.
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Stanco, L.
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Steinwagner, J.
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Tallada-Crespí, P.
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Taylor, A. N.
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Tereno, I.
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Toft, S.
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Toledo-Moreo, R.
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Torradeflot, F.
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Tutusaus, I.
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Valenziano, L.
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Valiviita, J.
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Vassallo, T.
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Verdoes Kleijn, G.
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Veropalumbo, A.
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Wang, Y.
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Weller, J.
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Zacchei, A.
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Zamorani, G.
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Zerbi, F. M.
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Zinchenko, I. A.
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Zucca, E.
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Allevato, V.
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Ballardini, M.
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Bolzonella, M.
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Bozzo, E.
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Burigana, C.
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Cabanac, R.
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Cappi, A.
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Di Ferdinando, D.
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Escartin Vigo, J. A.
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Gabarra, L.
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Huertas-Company, M.
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Martín-Fleitas, J.
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Matthew, S.
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Mauri, N.
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Metcalf, R. B.
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Pezzotta, A.
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Pöntinen, M.
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Porciani, C.
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Risso, I.
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Scottez, V.
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Sereno, M.
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Tenti, M.
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Viel, M.
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Wiesmann, M.
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Akrami, Y.
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Andika, I. T.
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Anselmi, S.
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Archidiacono, M.
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Atrio-Barandela, F.
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Benoist, C.
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Benson, K.
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Bertacca, D.
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Bethermin, M.
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Bisigello, L.
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Blanchard, A.
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Blot, L.
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Böhringer, H.
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Borgani, S.
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Brown, M. L.
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Bruton, S.
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Calabro, A.
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Camacho Quevedo, B.
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Caro, F.
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Carvalho, C. S.
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Castro, T.
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Cogato, F.
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Cooray, A. R.
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Cucciati, O.
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Davini, S.
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De Paolis, F.
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Desprez, G.
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Díaz-Sánchez, A.
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Diaz, J. J.
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Di Domizio, S.
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Diego, J. M.
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Duc, P.-A.
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Enia, A.
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Fang, Y.
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Ferrari, A. G.
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Ferreira, P. G.
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Finoguenov, A.
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Fontana, A.
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Franco, A.
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Ganga, K.
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García-Bellido, J.
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Gasparetto, T.
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Gautard, V.
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Gavazzi, R.
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Gaztanaga, E.
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Giacomini, F.
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Gianotti, F.
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Gozaliasl, G.
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Guidi, M.
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Gutierrez, C. M.
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Hall, A.
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Hartley, W. G.
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Hemmati, S.
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Hernández-Monteagudo, C.
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Hildebrandt, H.
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Hjorth, J.
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Kajava, J. J. E.
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Kang, Y.
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Kansal, V.
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Karagiannis, D.
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Kiiveri, K.
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Kirkpatrick, C. C.
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Kruk, S.
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Le Graet, J.
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Legrand, L.
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Lembo, M.
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Lepori, F.
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Leroy, G.
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Lesci, G. F.
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Lesgourgues, J.
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Leuzzi, L.
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Liaudat, T. I.
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Liu, S. J.
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Loureiro, A.
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Macias-Perez, J.
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Maggio, G.
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Magliocchetti, M.
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Mannucci, F.
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Maoli, R.
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Martins, C. J. A. P.
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Maurin, L.
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Miluzio, M.
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Monaco, P.
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Moretti, C.
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Morgante, G.
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Murray, C.
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Naidoo, K.
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Navarro-Alsina, A.
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Nesseris, S.
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Passalacqua, F.
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Paterson, K.
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Patrizii, L.
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Pisani, A.
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Potter, D.
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Quai, S.
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Radovich, M.
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Rocci, P.-F.
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Rodighiero, G.
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Sacquegna, S.
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Sahlén, M.
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Sanders, D. B.
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Sarpa, E.
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Scarlata, C.
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Schneider, A.
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Sciotti, D.
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Sellentin, E.
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Smith, L. C.
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Tanidis, K.
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Testera, G.
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Teyssier, R.
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Tosi, S.
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Troja, A.
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Tucci, M.
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Valieri, C.
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Venhola, A.
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Vergani, D.
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Verza, G.
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Vielzeuf, P.
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Walton, N. A.
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Scott, D.
Abstract
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Active galactic nuclei (AGN) are an important phase in galaxy evolution. However, they can be difficult to identify due to their varied observational signatures. Furthermore, to understand the impact of an AGN on its host galaxy, it is important to quantify the strength of the AGN with respect to the host galaxy. We developed a deep learning (DL) model to identify AGN in imaging data by deriving the contribution of the central point source. The model was trained with Euclidised mock galaxy images in which we artificially injected different levels of AGN, in the form of varying contributions of the point spread function (PSF). Our DL-based method can precisely and accurately recover the injected AGN contribution fraction, fPSF, with a mean difference between the predicted and true fPSF of −0.0078 and an overall root mean square error of 0.051. With this new method, we move beyond the simplistic AGN versus non-AGN classification and are able to precisely quantify the AGN contribution and study galaxy evolution across a continuous spectrum of AGN activity. We applied our method to a stellar-mass-limited sample (with M* ≥ 109.8 M⊙ and 0.5 ≤ z ≤ 2.0 ) selected from the first Euclid quick data release (Q1) and, using a threshold of fPSF > 0.2, we identified 61 432 ± 70 AGN over 63.1 deg2 (9.8 ± 0.1% of our sample). We compared these DL-selected AGN with AGN selected in the X-ray, mid-infrared (MIR), and via optical spectroscopy and investigated their overlapping fractions depending on different thresholds on the PSF contribution. We find that the overlap increases with increasing X-ray or bolometric AGN luminosity. We observe a positive correlation between the luminosity in the IE filter of the AGN and the host galaxy stellar mass, suggesting that supermassive black holes (SMBHs) generally grow faster (in absolute terms, i.e. the luminosity of the PSF component is larger) in more massive galaxies. Moreover, the mean relative contribution of the AGN is higher in the quiescent galaxy population than in the star-forming population. In terms of absolute power, starburst galaxies, as well as the most massive galaxies (across the star-formation main sequence), tend to host the most luminous AGN, indicating concomitant assembly of the SMBH and the host galaxy.
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