Overdense fireworks in GOODS-N: Unveiling a record number of massive dusty star-forming galaxies at z ∼ 5.2 with the N2CLS

¹ Aix Marseille Univ., CNRS, CNES, LAM (Laboratoire d’Astrophysique de Marseille) Marseille, France
² Department of Astronomy, University of Geneva Chemin Pegasi 51 1290 Versoix, Switzerland
³ Institut de Radioastronomie Millimétrique (IRAM) 300 Rue de la Piscine 38400 Saint-Martin-d’Hères, France
⁴ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange Nice, France
⁵ School of Physics and Astronomy, Cardiff University Queen’s Buildings The Parade Cardiff CF24 3AA, UK
⁶ Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM F-91191 Gif-sur-Yvette, France
⁷ Institut de Radioastronomie Millimétrique (IRAM), Avenida Divina Pastora 7 Local 20 E-18012 Granada, Spain
⁸ Institut Néel, CNRS, Université Grenoble Alpes Grenoble, France
⁹ Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550 67000 Strasbourg, France
¹⁰ Astronomy Centre, Department of Physics and Astronomy, University of Sussex Brighton BN1 9QH, UK
¹¹ Univ. Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 53 Avenue des Martyrs 38000 Grenoble, France
¹² Dipartimento di Fisica, Sapienza Università di Roma Piazzale Aldo Moro 5 I-00185 Roma, Italy
¹³ Univ. Grenoble Alpes, CNRS, IPAG 38000 Grenoble, France
¹⁴ Institute for Research in Fundamental Sciences (IPM), School of Astronomy Tehran, Iran
¹⁵ Centro de Astrobiología (CSIC-INTA) Torrejón de Ardoz 28850 Madrid, Spain
¹⁶ Aix Marseille Univ., CNRS/IN2P3, CPPM Marseille, France
¹⁷ National Observatory of Athens, Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, Ioannou Metaxa and Vasileos Pavlou GR-15236 Athens, Greece
¹⁸ Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis GR-15784 Zografos Athens, Greece
¹⁹ High Energy Physics Division, Argonne National Laboratory 9700 South Cass Avenue Lemont IL 60439, USA
²⁰ LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC 75014 Paris, France
²¹ Institute of Space Sciences (ICE), CSIC, Campus UAB Carrer de Can Magrans s/n E-08193 Barcelona, Spain
²² ICREA Pg. Lluís Companys 23 Barcelona, Spain
²³ IRAP, CNRS, Université de Toulouse, CNES, UT3-UPS Toulouse, France
²⁴ Cosmic Dawn Center (DAWN) Copenhagen, Denmark
²⁵ Niels Bohr Institute, University of Copenhagen Jagtvej 128 DK-2200 Copenhagen N, Denmark
²⁶ Dipartimento di Fisica, Università di Roma ‘Tor Vergata’ Via della Ricerca Scientifica 1 I-00133 Roma, Italy
²⁷ School of Physics and Astronomy, University of Leeds Leeds LS2 9JT, UK
²⁸ Institut d’Astrophysique de Paris, CNRS (UMR7095) 98 bis boulevard Arago 75014 Paris, France
²⁹ University of Lyon, UCB Lyon 1, CNRS/IN2P3, IP2I 69622 Villeurbanne, France
³⁰ University Federico II Naples, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 13 June 2025
Accepted: 12 November 2025

Abstract

High-density environments, such as early galaxy overdensities, play a critical role in hierarchical structure formation and galaxy evolution, providing an ideal setting for accelerated galaxy growth. The GOODS-N overdensity at z ≃ 5.2 has long been known, but its full extent and richness have only recently been revealed by JWST observations. It is highly elongated along the line of sight, spanning nearly 30 cMpc. We investigated its dusty galaxy population using the NIKA2 Cosmological Legacy Survey (N2CLS). Within this overdensity, we identify five luminous dusty starbursts that are spectroscopically confirmed, along with three additional candidates supported by robust photometric redshifts. Three of the spectroscopically confirmed galaxies (N2GN_1_01, 06, and 23, known as GN10, HDF850.1, and S3, respectively) had already been recognised as members of this exceptional structure. We report the discovery of N2GN_1_13 at z_spec = 5.182, a massive dusty star-forming galaxy that we confirmed as part of the overdensity through targeted NOEMA follow-up observations of the N2CLS. In addition, by combining our analysis with JWST/FRESCO data, we identified another dusty galaxy at z_spec = 5.201 (N2GN_1_61). The eight dusty galaxies are massive (with a median stellar mass of ∼9 × 10¹⁰ M_⊙) and highly obscured (with a median A_V of ∼3.3) and caught in a short-lived yet extreme starburst phase at z ∼ 5.2. Their high star formation rates (with a median of ∼590 M_⊙ yr⁻¹), efficient baryon to stellar mass conversion (ϵ_★ > 20% for 75% of the sample), and substantial gas reservoirs and dust content suggest rapid evolution and imminent quenching. Six of these galaxies reside in overdense filaments; the remaining two may trace new distinct structures, which will have to be spectroscopically confirmed. These few dusty galaxies dominate the star formation within the overdensity, contributing more than the numerous Hα emitters, and surpassing the cosmic average star formation rate density for this epoch. The presence of numerous very massive, dusty, and intensely star-forming galaxies at z ∼ 5.2 shows that rapid stellar and dust mass assembly was already underway within the first billion years of cosmic history in overdense environments. Their properties, likely driven by efficient gas inflows along cosmic filaments in protocluster regions, suggest an accelerated evolution that current models and simulations have difficulty reproducing.