Letter to the Editor

Spectroscopic confirmation of a dust-obscured, possibly metal-rich dwarf galaxy at z ∼ 5

¹ INAF, Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
² Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Via Marzolo 8, 35131 Padova, Italy
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ NSF’s National Optical-Infrared Astronomy Research Laboratory, 950 N. Cherry Ave., Tucson, AZ, 85719 USA
⁵ Astrophysics Science Division, NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD, 20771 USA
⁶ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00078 Monte Porzio Catone, Italy
⁷ Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA, 16802 USA
⁸ Institute for Computational and Data Sciences, The Pennsylvania State University, University Park, PA, 16802 USA
⁹ Institute for Gravitation and the Cosmos, The Pennsylvania State University, University Park, PA, 16802 USA
¹⁰ Centro de Astrobiología (CAB), CSIC-INTA, Ctra de Ajalvir km 4, Torrejón de Ardoz, 28850 Madrid, Spain
¹¹ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
¹² INAF-Osservatorio di Astrofisica e Scienza dello Spazio, via Gobetti 93/3, I-40129 Bologna, Italy
¹³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 USA
¹⁴ Physics & Astronomy Department, University of Louisville, 40292 KY, Louisville, USA
¹⁵ INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00078 Monte Porzio Catone, Italy
¹⁶ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA, 02138 USA
¹⁷ Black Hole Initiative, Harvard University, 20 Garden St, Cambridge, MA, 02138 USA
¹⁸ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁹ Astronomy Centre, University of Sussex, Falmer, Brighton, BN1 9QH UK
²⁰ Institute of Space Sciences and Astronomy, University of Malta, Msida, MSD 2080 Malta
²¹ Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
²² Cosmic Frontier Center, The University of Texas at Austin, Austin, TX, USA
²³ Laboratory for Multiwavelength Astrophysics, School of Physics and Astronomy, Rochester Institute of Technology, 84 Lomb Memorial Drive, Rochester, NY, 14623 USA
²⁴ Department of Physics and Astronomy, Texas A&M University, College Station, TX, 77843-4242 USA
²⁵ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX, 77843-4242 USA
²⁶ ESA/AURA Space Telescope Science Institute, USA

^⋆ Corresponding author; laura.bisigello@inaf.it

Received: 14 October 2024
Accepted: 13 December 2024

Abstract

We present the first spectroscopic confirmation of a dust-obscured dwarf galaxy, CEERS-14821. The analysis was performed by combining JWST NIRCam broadband photometry and NIRSpec/PRISM spectroscopic data. From the detection of multiple rest-frame optical lines, we derive that CEERS-14821 is located at z = 4.883 ± 0.003. Moreover, from a secure detection of the H_α and H_β, we derive that the galaxy has a dust extinction ranging from A_V = 2.2_−0.6^+0.5 to A_V = 3.4_−0.9^+0.7, depending on the assumed reddening law. This value is extremely large given that we estimated a low stellar mass, that is, log₁₀(M/M_⊙) = 8.17_−0.04^+0.05 or log₁₀(M/M_⊙) = 8.65_−0.05^+0.06, based on two different dust extinction laws. Moreover, the combination of different metallicity tracers and the spectro-photometric fit suggests that the galaxy may also be metal-rich, with 12 + log₁₀(O/H)> 8.3, but a low metallicity value cannot be totally ruled out. The high metallicity value would be above the expectation based on the mass-metallicity relation. Both metallicity estimations are above the expectations based on the fundamental mass-metallicity relation since CEERS-14821 is going through a burst of star formation. The constraints on a possible active galactic nucleus presence are limited and loose, but they point towards a possible non-dominant contribution (f_AGN <  0.5 with respect to the total dust luminosity). Based on the rest-frame optical images, this source has a size compatible with galaxies of similar stellar masses and at similar redshifts. Finally, CEERS-14821 may be part of a larger galaxy overdensity, but there are no other galaxies closely interacting with it (within 30 Mpc).