GA-NIFS: The highly overdense system BR1202-0725 at z ∼ 4.7

A double active galactic nucleus with fast outflows plus eight companion galaxies

¹ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
² INAF – Osservatorio Astrofisco di Arcetri, largo E. Fermi 5, 50127 Firenze, Italy
³ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, E-28850 Madrid, Spain
⁴ European Space Agency, c/o STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ University of Oxford, Department of Physics, Denys Wilkinson Building, Keble Road, Oxford OX13RH, United Kingdom
⁶ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
⁷ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁸ Cavendish Laboratory - Astrophysics Group, University of Cambridge, 19 JJ Thomson Avenue, Cambridge CB3 0HE, UK
⁹ Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstraße 1, 85748 Garching, Germany
¹⁰ Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto F.no (Firenze), Italy

^⋆ Corresponding author: sandra.zamoraarenal@sns.it

Received: 29 November 2024
Accepted: 1 July 2025

Abstract

Distant quasars (QSOs) in galaxy overdensities are considered key actors in the evolution of the early Universe. In this work, we performed an analysis of the kinematic and physical properties of the BR1202-0725 system at z ∼ 4.7, one of the most overdense fields known in the early Universe, consisting of a QSO, a sub-millimetre galaxy (SMG), and three Lyman-α emitters. We used data from the JWST/NIRSpec integral field unit to analyse the rest-frame optical emission of each source in the system. Based on the continuum and Balmer line emission, we estimated a bolometric luminosity of log(L_bol/[erg s⁻¹]) = 47.2 ± 0.4 and a black hole mass of log(M_BH/M_⊙) = 10.1 ± 0.5 for the QSO, which are consistent with previous measurements obtained with ground-based observations. The NIRSpec spectra of the SMG revealed, instead, unexpected [O III] and Hα+[N II] profiles. The overall [O III] line profile is blueshifted by more than 700 km s⁻¹relative to the systemic velocity of the galaxy. Additionally, both the [O III] and Hα+[N II] lines show prominent broad (∼1300 km s⁻¹), blueshifted wings associated with outflowing ionized gas. The analysis of NIRSpec and X-ray observations indicates that the SMG likely hosts an accreting supermassive black hole, which is supported by the following results: (i) the excitation diagnostic diagram is consistent with ionization from an active galactic nucleus (AGN); (ii) the X-ray luminosity is higher than 10⁴⁴ erg s⁻¹; and (iii) it hosts a fast outflow (v_out ∼ 5000 km s⁻¹), comparable to the ones observed in luminous QSOs. Therefore, the QSO-SMG pair of BR1202-0725 represents one of the highest-redshift double AGNs found to date, with a projected separation of 24 kpc. Finally, we investigated the environment of this system and found four new galaxies, detected in both [O III] and Hαemission, at the same redshift of the QSO and within a projected distance of 5 kpc from it. This overdense system includes at least ten galaxies in a field of view of only 980 kpc².