Program: GN-2015B-Q-5

For more than a decade sub-millimetre galaxies (SMGs) have been heralded as the most active sites of star formation in the high redshift Universe. However, the coarse resolution (~18'') of single-dish submm surveys means that it has been unclear whether the submm flux arises from a single source, or from a blend of multiple SMGs. In ALMA Cy1 and ongoing SMA-large programs we observed of 49 bright submm sources in the Ultra Deep Survey (UDS) field, resolving 22 single-dish sources into multiple components (>2 SMGs). We request GNIRS spectroscopy to determine redshifts for the K-brightest SMGs identified in these ALMA/SMA maps to determine if the multiplicity arises due to physical associations or line of sight projections. (It is still far too expensive to consider this project with CO lines directly with ALMA). These observations will be used to test competing models of galaxy formation, which variously predict that the intense star-formation in SMGs is major-merger driven or a secular burst in an isolated disk.