James Webb Space Telescope Feed Post

Hidden Giants in JWST's PEARLS: An Ultramassive z = 4.26 Submillimeter Galaxy that Is Invisible to HST

A three-color JWST NIRCam image of a 100' × 100' region (north at the top, east to the left) around the z = 0.35 cluster A 1489 (where F090W+F150W is shown as blue, F200W+F277W is green, and F356W+F444W is red). Signal-to-noise contours are shown, representing the SCUBA-2 850 µm emission (starting at 5s, in 5s increments, 14farcs5 FWHM beam), the SCUBA-2 450 µm emission (3s and 4s, 7farcs5 FWHM beam), and the NOEMA 3 mm continuum emission (10s, ~5' FWHM beam). Note that 850.1 and 850.2 are the two bright sources visible at 450 µm, 850 µm, and 3 mm to the northeast of the cluster core, which is identified by several bright elliptical galaxies, as well as associated strong lensing features. The counterparts to these sources are unambiguously identified using the higher-resolution SMA 880 µm observations shown in Figure 2. Abstract: We present a multiwavelength analysis using the Submillimeter Array (SMA), James Clerk Maxwell Telescope, NOEMA, JWST, the Hubble Space Telescope (HST), and the Spitzer Space Telescope of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A 1489. These SMA-located sources both lie at z = 4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at ? 2 µm, even with deep JWST/NIRCam observations. We investigate their stellar, interstellar medium, and dynamical properties, including a pixel-level spectral energy distribution analysis to derive subkiloparsec-resolution stellar-mass and AV maps. We find that 850.1 is one of the most massive and highly obscured, AV ~ 5, galaxies known at z > 4 with M* ~1011.8M? (likely forming at z > 6), and 850.2 is one of the least massive and least obscured, AV ~ 1, members of the z > 4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z ? 3–4 based on imaging at ? 2 µm, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar-mass distribution, ${R}_{{\rm{e}}}^{\mathrm{mass}}$ ~1 kpc, but its expected evolution means that it matches both the properties of massive, quiescent galaxies at z ~ 1.5 and ultramassive early-type galaxies at z ~ 0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature that we link to the active dynamical environment it resides within.