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Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter galaxy that is invisible to HST Published: 6/28/2023 12:15:57 PM Updated: 6/28/2023 12:15:57 PM

Paper abstract: We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, andSST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen throughthe massive cluster lens A1489. These SMA-located sources both lie at z=4.26and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-breakgalaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCamobservations. We investigate their stellar, ISM, and dynamical properties,including a pixel-level SED analysis to derive sub-kpc-resolution stellar-massand 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*~10^11.8 Mo (likely forming at z>6), and850.2 is one of the least massive and least obscured, Av~1, members of the z>4dusty star-forming population. The diversity of these two dust-mass-selectedgalaxies illustrates the incompleteness of galaxy surveys at z>3-4 based onimaging at <2um, the longest wavelengths feasible from HST or the ground. Theresolved mass map of 850.1 shows a compact stellar mass distribution,Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches boththe properties of massive, quiescent galaxies at z~1.5 and ultra-massiveearly-type galaxies at z~0. We suggest that 850.1 is the central galaxy of agroup 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 which welink to the active dynamical environment it resides within.