Revealing the hidden stellar emission in the highest-fidelity ALMA-mapped submillimeter galaxies

Twenty years after their discovery, the nature of the most highly star-forming galaxies in the universe remains a mystery. Despite forming stars at 100s-1000s M_sol yr^-1, these z~2.5 submillimeter-bright galaxies (SMGs) are notoriously difficult to study with optical telescopes due to their extreme dust obscuration, rendering them faint/invisible even in deep HST H-band imaging, and leading to decades of debate on whether major mergers are necessary to trigger their starbursts. Recently, ALMA has revolutionized the field by revealing the obscured star formation in SMGs in unprecedented detail. Here we propose NIRCam+MIRI imaging at 2-7um of 12 SMGs with unrivaled high-S/N ALMA continuum imaging, which span a range in redshift and SFRs reflective of the larger SMG population. By detecting and resolving the stellar emission at rest-frame ~500nm to (crucially) 2um — a jump of a factor of 5 in rest-wavelength over the HST H-band — these observations will put first constraints on the underlying morphologies of the stellar emission in these sources, and at a resolution that is perfectly matched to that of the high-S/N ALMA imaging. This proposal will provide maps of resolved stellar mass and star formation rate (and thus, the specific star formation rate), and will yield first reliable total masses for this historically unconstrained population. These observations will provide the context necessary to interpret the ALMA-revealed star formation and its ability to morphologically transform SMGs into their proposed descendants - massive local elliptical galaxies.