Program: GS-2021A-Q-120

After 7 cycles of ALMA observations, we have now obtained a spectroscopically complete sample of 81 SPT mm-wave selected, gravitationally lensed high-redshift submm galaxies. Of these lensed systems, 9 do not have J and K band imaging. We propose FLAMINGOS2 imaging to study the foreground lenses, to enable precision modelling of the lensed systems, and study the lens galaxies themselves. The gravitationally lensing mass contrasted with the stellar mass distribution provides an unique laboratory for understanding massive galaxy profiles. We also propose Flamingos 2 longslit spectroscopy to measure redshifts of 8 K band detected foreground lens galaxies around redshift 1. This proposal will contribute to the legacy value of SPT-SMG sample which has complete data from ALMA, Herschel, APEX and Spitzer.