16504

Dense protoclusters of bright submillimeter galaxies are the suspected progenitors of today.s massive clusters comma but the mechanisms that govern their triggering and transition to compact quiescent galaxies by z virgul 2 are not well understood. These processes are hinted at by millimeter spectral line profiles comma but are only fully resolved at sub-arcsecond scales comma which cannot be imaged efficiently with ground-based telescopes in the Northern hemisphere. We propose to constrain the morphology of the stars in the two submillimeter-brightest galaxies in a newly identified comma spectroscopically confirmed protocluster at z = 3.14. This requires 5 total orbits with WFC3-IR comma with 3 orbits with F110W and 2 orbits with F160W. The protocluster lies in the GOODS-North and has extensive multi-wavelength coverage comma but is just outside the coverage of HST-ACS and WFC3 from the original GOODS and CANDELS surveys comma such that no sufficiently high-resolution imaging of this field currently exists. The two galaxies have spectroscopic redshifts from CO line scans with NOEMA comma but their CO(5-4) line profiles are different comma suggesting different stages or mechanisms of triggering. The 0.15.. resolution of the proposed observations will resolve close mergers and-or compact stellar counterparts. Our virgul9 square arminute coverage will also serendipitously detect the near-IR counterparts of many fainter submillimeter galaxies in this dense field. The identification of advanced mergers or compact stellar counterparts in these galaxies comma which can trace ongoing triggering or quenching comma respectively comma will be used to prioritize targets for high-resolution millimeter interferometric follow-up.