CEERS Key Paper. IV. A Triality in the Nature of HST-dark Galaxies


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The new capabilities that JWST offers in the near- and mid-infrared (IR) are used to investigate in unprecedented detail the nature of optical/near-IR-faint, mid-IR-bright sources, with HST-dark galaxies among them. We gather JWST data from the CEERS survey in the Extended Groth Strip, jointly with HST data, and analyze spatially resolved optical-to-mid-IR spectral energy distributions to estimate photometric redshifts in two dimensions and stellar population properties on a pixel-by-pixel basis for red galaxies detected by NIRCam. We select 138 galaxies with F150W − F356W > 1.5 mag and F356W < 27.5 mag. The nature of these sources is threefold: (1) 71% are dusty star-forming galaxies (SFGs) at 2 < z < 6 with $9\lt \mathrm{log}{M}_{\star }/{M}_{\odot }\lt 11$ and a variety of specific SFRs (100 Gyr−1); (2) 18% are quiescent/dormant (i.e., subject to reignition/rejuvenation) galaxies (QGs) at 3 < z < 5, with $\mathrm{log}{M}_{\star }/{M}_{\odot }\sim 10$ and poststarburst mass-weighted ages (0.5–1.0 Gyr); and (3) 11% are strong young starbursts with indications of high equivalent width emission lines (typically, [O iii]+Hβ) at 6 < z < 7 (XELG-z6) and $\mathrm{log}{M}_{\star }/{M}_{\odot }\sim 9.5$. The sample is dominated by disk-like galaxies with remarkable compactness for XELG-z6 (effective radii smaller than 0.4 kpc). Large attenuations in SFGs, 2 < A(V) < 5 mag, are found within 1.5 times the effective radius, approximately 2 kpc, while QGs present A(V) ∼ 0.2 mag. Our SED-fitting technique reproduces the expected dust emission luminosities of IR-bright and submillimeter galaxies. This study implies high levels of star formation activity between z ∼ 20 and z ∼ 10, where virtually 100% of our galaxies had already formed 108 M⊙, 60% had assembled 109 M⊙, and 10% up to 1010 M⊙ (in situ or ex situ).
Original languageEnglish
Article numberL16
JournalThe Astrophysical Journal Letters
Issue number1
Publication statusPublished - 1 Mar 2023

Bibliographical note

We would like to thank Prof. Giulia Rodighiero for carefully and very constructively reviewing the manuscript. P.G.P.-G. acknowledges support from Spanish Ministerio de Ciencia e Innovación MCIN/AEI/10.13039/501100011033 through grant PGC2018-093499-B-I00. Á.G.A. acknowledges the support of the Universidad Complutense de Madrid through the predoctoral grant CT17/17-CT18/17. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Centro de Astrobiología (CAB), CSIC-INTA, partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). This work is based on observations carried out under project number W20CK with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

The data used in this paper come from the CEERS project and are available and documented at ceers.github.io/dr05.html and at MAST via 10.17909/z7p0-8481. See Bagley et al. (2022) for details.


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