Program: GS-2015B-Q-51

We propose to observe 5 strongly lensed, dusty, star forming galaxies with GMOS-S/IFU to map stellar absorption lines in the foreground lenses. These observations support an ALMA Cy 2 program (A-rated) in progress to detect dark matter subhalos in the lens galaxies using gravitationally-induced perturbations they cause on the images of background sources. With detailed simulations, we have shown that ALMA is capable of efficiently detecting subhalos in these systems, if the abundance of subhalos is in agreement with LCDM predictions. We have built and tested a complete pipeline to search for and detect subhalos using ALMA data, which will incorporate the absorption line velocity fields mapped by GMOS-IFU. We will constrain the slope of the lensing potential (which requires mass measurements at multiple radii), which is a crucial parameter for the lens models and substructure detection.