Behind the dust veil: A panchromatic view of an optically dark galaxy at z = 4.82
Journal article, 2025
Optically dark dusty star-forming galaxies (DSFGs) play an essential role in massive galaxy formation at early cosmic time; however, their nature remains elusive. Here, we present a detailed case study of all the baryonic components of a z = 4.821 DSFG, XS55. Selected from the ultra-deep COSMOS-XS 3 GHz map with a red SCUBA-2 450 μm/850 μm colour, XS55 was followed up with ALMA 3 mm line scans and spectroscopically confirmed to be at z = 4.821 via detections of the CO(5-4) and [CI](1-0) lines. JWST/NIRCam imaging reveals that XS55 is a F150W drop-out with a red F277W/F444W colour and a complex morphology: a compact central component embedded in an extended structure with a likely companion. XS55 is tentatively detected in X-rays with both Chandra and XMM-Newton, suggesting an active galactic nucleus nature. By fitting a panchromatic spectral energy distribution spanning from near-infrared to radio wavelengths, we reveal that XS55 is a massive main-sequence galaxy with a stellar mass of M∗ = (5 ± 1)×1010 M⊙ and a star formation rate of SFR = 540 ± 177 M⊙ yr- 1. The dust of XS55 is optically thick in the far-infrared with a surprisingly cold dust temperature of Tdust = 33 ± 2 K, making XS55 one of the coldest DSFGs at z > 4 known to date. This work unveils the nature of a radio-selected F150W drop-out, suggesting the existence of a population of DSFGs hosting active black holes embedded in optically thick dust.
Galaxies: general
Galaxies: ISM
Galaxies: active
Author
Nikolaj B. Sillassen
Technical University of Denmark (DTU)
Cosmic Dawn Center (DAWN)
S. Jin
Technical University of Denmark (DTU)
Cosmic Dawn Center (DAWN)
Georgios E. Magdis
Niels Bohr Institute
Technical University of Denmark (DTU)
Cosmic Dawn Center (DAWN)
J. Hodge
Leiden University
Raphael Gobat
Pontificia Universidad Católica de Valparaíso
Emanuele Daddi
University Paris-Saclay
Kirsten Knudsen
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Alexis Finoguenov
University of Helsinki
E. Schinnerer
Max Planck Society
Wei Hao Wang
Academia Sinica
Zhen Kai Gao
Academia Sinica
J. R. Weaver
University of Massachusetts
H. Algera
National Astronomical Observatory of Japan
Academia Sinica
Hiroshima University
Irham T. Andika
Max Planck Society
Technical University of Munich
Malte Brinch
University of Valparaíso
C. C. Chen
Academia Sinica
R. Cochrane
Columbia University
University of Edinburgh
A. F.M. Enia
Istituto nazionale di astrofisica (INAF)
University of Bologna
A. Faisst
California Institute of Technology (Caltech)
S. Gillman
Cosmic Dawn Center (DAWN)
Technical University of Denmark (DTU)
Carlos Gomez-Guijarro
University Paris-Saclay
Ghassem Gozaliasl
University of Helsinki
Aalto University
Christopher C. Hayward
Flatiron Institute
V. Kokorev
The University of Texas at Austin
Maya Merchant
Cosmic Dawn Center (DAWN)
Niels Bohr Institute
Francesca Rizzo
University of Groningen
Margherita Talia
Istituto nazionale di astrofisica (INAF)
University of Bologna
F. Valentino
Cosmic Dawn Center (DAWN)
Technical University of Denmark (DTU)
David Blánquez-Sesé
Cosmic Dawn Center (DAWN)
Technical University of Denmark (DTU)
Anton M. Koekemoer
Space Telescope Science Institute (STScI)
Benjamin Magnelli
University Paris-Saclay
R. Michael Rich
University of California
Marko Shuntov
Cosmic Dawn Center (DAWN)
Niels Bohr Institute
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 693 A309The Origin and Fate of Dust in Our Universe
Knut and Alice Wallenberg Foundation (KAW 2019.0443), 2020-06-01 -- 2023-05-31.
Knut and Alice Wallenberg Foundation (KAW 2020.0081), 2021-07-01 -- 2026-06-30.
Subject Categories (SSIF 2025)
Other Physics Topics
Astronomy, Astrophysics, and Cosmology
DOI
10.1051/0004-6361/202452932