Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at z about 7.7

arXiv:2607.03430 · astro-ph.GA, astro-ph.CO · Submitted 2026-07-03 · Read on arXiv

S. Belladitta, R. Decarli, E. Bañados, F. Walter, D. Yang, F. Guarneri, K. Jahnke, S. Bisogni, S. E. I. Bosman, X. Fan, Y. Fu, J. F. Hennawi, Y. Matsuoka, D. J. Mortlock, M. Onoue, J. -T. Schindler, L. Spinoglio, D. Stern, F. Wang, G. Vietri, C. J. Willott, J. Wolf, J. Yang, R. A. A. Bowler, K. I. Caputi, D. L. Clements, C. M. Gutierrez, H. J. A. Rottgering, D. Scott, F. Shankar, G. Zamorani, A. -C. Eilers, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, J. -G. Cuby, A. Da Silva, H. Degaudenzi, G. De Lucia, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, R. Laureijs, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, R. C. Nichol, S. -M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, H. -W. Rix, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, F. M. Zerbi, E. Zucca, J. García-Bellido, J. Martín-Fleitas, P. Monaco, V. Scottez, M. Viel

astro-ph.GA, astro-ph.CO

Submitted: 2026-07-03

Comments: 12 pages, 6 figures, 1 table, Accepted for Publication in A&A

DOI: 10.1051/0004-6361/202659319

License: http://creativecommons.org/licenses/by/4.0/

The gist: Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic

Terminology

Abstract

Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of the z about 7.7 quasar EUCL,J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [CII] 158 mu m and cold dust emission in a quasar host to date. The [CII] emission line sets the systemic redshift at z=7.6980 plus or minus0.0004. The source exhibits luminosities of L FIR=3.6 times10 12,L and L[CII]=2 times10 9,L, respectively, a dust mass of 1.4 times 10 8,M, and a dynamical mass in the range 0.33-1.3 times10 10,M. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV (M 1450=-24.06) than previously known z about7.5 quasars (<M 1450 > about- 26.5), EUCL,J125308.55+705432.3 exhibits the brightest [CII] emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate >250,M, yr-1, consistent with recent findings that UV-faint quasars at z>6 preferentially reside in [CII]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combining Euclid's wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible.

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