Ultrahigh-redshift or closer-by, dust-obscured galaxies?

Deciphering the nature of faint, previously missed F200W dropouts in CEERS

¹ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35131 Padova, Italy
² INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
⁴ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ 85719, USA
⁵ INAF, Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monteporzio Catone, Roma, Italy
⁶ Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁷ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843-4242, USA
⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
⁹ Departamento de Física Teórica, Atómica y Öptica, Universidad de Valladolid, 47011 Valladolid, Spain
¹⁰ Instituto de Astrofísica e Ciências do Espaço, Universidade de Lisboa, OAL, Tapada da Ajuda, PT1349-018 Lisbon, Portugal
¹¹ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
¹² Institute for Physics, Laboratory for Galaxy Evolution and Spectral modelling, École Polytechnique Fédérale de Lausanne, Observatoire de Sauverny, Chemin Pégasi 51, 1290 Versoix, Switzerland
¹³ INAF, Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
¹⁴ Department of Physics & Astronomy, University of Louisville, Natural Science Building 102, Louisville, KY 40292, USA
¹⁵ Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
¹⁶ SISSA, Via Bonomea 265, 34136 Trieste, Italy
¹⁷ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁸ IRA-INAF/Italian ARC, Via Gobetti 101, 40129 Bologna, Italy
¹⁹ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
²⁰ Black Hole Initiative, Harvard University, 20 Garden St, Cambridge, MA 02138, USA
²¹ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, E-28850, Madrid, Spain
²² Astronomy Centre, Department of Physics & Astronomy, University of Sussex, Brighton BN1 9RH, United Kingdom
²³ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁴ Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003, USA
²⁵ Department of Physics, 196 Auditorium Road, Unit 3046, University of Connecticut, Storrs, CT 06269 Storrs, Connecticut, USA
²⁶ Aix Marseille Université, CNRS, CNES, LAM, Marseille, France
²⁷ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY 14623, USA
²⁸ Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045, USA
²⁹ Department of Physics and Astronomy, Colby College, Waterville, ME 04901, USA
³⁰ ESA/AURA Space Telescope Science Institute, Baltimore, Maryland, USA
³¹ Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV, Groningen, The Netherlands
³² SRON Netherlands Institute for Space Research, Postbus 800, 9700 AV, Groningen, The Netherlands

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Received: 3 February 2025
Accepted: 13 January 2026

Abstract

Context. The James Webb Space Telescope (JWST) is revolutionizing our understanding of the Universe by unveiling faint, near-infrared dropouts previously beyond our reach, ranging from exceptionally dusty sources to galaxies up to redshift z ∼ 14.

Aims. In this paper, we identify F200W-dropout objects in the Cosmic Evolution Early Release Science (CEERS) survey that are absent from existing catalogs. Our selection method can effectively identify obscured low-mass (logM_*/M_⊙ ≤ 9) objects at z ≤ 6, massive dust-rich sources up to z ∼ 12, and ultrahigh-redshift (z > 15) candidates. Our goal is to uncover promising targets for further studies using deep mid-infrared imaging and/or spectroscopic follow-ups.

Methods. We utilize two photometric catalogs optimized for detecting faint, red objects. Primarily relying on NIRCam photometry from the latest CEERS data release and supplementing with mid-infrared/(sub)millimeter data when available, our analysis pipeline combines multiple SED-fitting codes, star formation histories, and the novel CosMix tool for astronomical stacking to maximize available photometric information.

Results. Our work highlights three 2 < z < 3 dusty dwarf galaxies that have higher masses compared to the typical dusty dwarfs previously identified in CEERS. Additionally, we reveal five faint sources with a significant probability of lying above z > 15, with best-fit masses compatible with Λ cold dark matter and a standard baryon-to-star conversion efficiency. We exploit these candidates to compute the z ∼ 17 UV luminosity function, finding estimates in good agreement with other similar studies. Their bimodal redshift probability distributions suggest they could also be z < 1.5 dwarf galaxies with extreme dust extinction. We also identify a strong line emitter galaxy at z ∼ 5 mimicking the near-infrared emission of a z ∼ 13 galaxy.

Conclusions. Our sample holds promising candidates for future follow-ups. Confirming ultrahigh-redshift galaxies or lower-redshift dusty dwarfs will offer valuable insights into early galaxy formation, evolution with their central black holes and the nature of dark matter, and/or cosmic dust production mechanisms in low-mass galaxies, and will help us to understand degeneracies and contamination in high-redshift object searches.