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

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 less than or similar to 2 mu m, 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 A(V) maps. We find that 850.1 is one of the most massive and highly obscured, A(V) similar to 5, galaxies known at z > 4 with M-* similar to 10(11.8)M(circle dot) (likely forming at z > 6), and 850.2 is one of the least massive and least obscured, A(V) similar to 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 greater than or similar to 3-4 based on imaging at less than or similar to 2 mu m, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar-mass distribution, R-e(mass) similar to 1 kpc, but its expected evolution means that it matches both the properties of massive, quiescent galaxies at z similar to 1.5 and ultramassive early-type galaxies at z similar to 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.