JWST Insight into a Lensed HST-dark Galaxy and Its Quiescent Companion at z = 2.58

Vasily Kokorev, Shuowen Jin, Georgios E. Magdis, Karina I. Caputi, Francesco Valentino, Pratika Dayal, Maxime Trebitsch, Gabriel Brammer, Seiji Fujimoto, Franz Bauer, Edoardo Iani, Kotaro Kohno, David Blánquez Sesé, Carlos Gómez-Guijarro, Pierluigi Rinaldi, Rafael Navarro-Carrera

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Using the novel James Webb Space Telescope (JWST)/NIRCam observations in the A2744 field, we present a first spatially resolved overview of a Hubble Space Telescope (HST)-dark galaxy, spectroscopically confirmed at z = 2.58 with magnification μ ≈ 1.9. While being largely invisible at ∼1 μm with NIRCam, except for sparse clumpy substructures, the object is well detected and resolved in the long-wavelength bands with a spiral shape clearly visible in F277W. By combining ancillary Atacama Large Millimeter/submillimeter Array (ALMA) and Herschel data, we infer that this object is an edge-on dusty spiral with an intrinsic stellar mass log (M*/M) ∼ 11.3 and a dust-obscured star formation rate ∼300 M yr−1. A massive quiescent galaxy (log (M*/M) ∼ 10.8) with tidal features lies 20 away (r ∼ 9 kpc), at a consistent redshift as inferred by JWST photometry, indicating a potential major merger. The dusty spiral lies on the main sequence of star formation, and shows high dust attenuation in the optical (3 < AV < 4.5). In the far-infrared, its integrated dust spectral energy distribution is optically thick up to λ0 ∼ 500 μm, further supporting the extremely dusty nature. Spatially resolved analysis of the HST-dark galaxy reveals a largely uniform AV ∼ 4 area spanning ∼57 kpc2, which spatially matches to the ALMA 1 mm continuum emission. Accounting for the surface brightness dimming and the depths of current JWST surveys, unlensed analogs of the HST-dark galaxy at z > 4 would be only detectable in F356W and F444W in an UNCOVER-like survey, and become totally JWST-dark at z ∼ 6. This suggests that detecting highly attenuated galaxies in the Epoch of Reionization might be a challenging task for JWST.
Original languageEnglish
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 2023


  • Active galaxies
  • Disk galaxies


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