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

Abstract

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 μ m 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 2.″0 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 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.

Keywords

• Active galaxies
• Disk galaxies