Program: GN-2015A-Q-55

We have identified candidate 350 - 650 K late-T and Y brown dwarfs at the faint limits of the WISE survey, using WISE multiple measurements and photometric profile fits to identify non-variable point sources detected only at 4.6 um (W2). Gemini North and South time in 13B and 14A was used to follow up 78 of these candidates with near-infrared photometry and spectroscopy. To date, we have spectroscopically confirmed five new T8-9 dwarfs and one new Y0 dwarf. We propose in 15A to essentially complete the follow up, by obtaining additional near-infrared data for 24 of the targets observed at Gemini, which are likely to be very cool brown dwarfs. Only 21 Y dwarfs are currently known. Increasing this number is important for sampling the wide range in cloud properties, surface gravity and chemical composition that is likely to exist, and which is suggested by the current dataset, in order to improve models. A census of such objects constrains the substellar mass function, the low-mass cut-off for star formation, and the Galactic star-formation rate. This work enables the WISE mission to reach its full potential for one of its key goals: discovery of the nearest and coolest brown dwarfs.