“Old Galaxies, New Surprises”

I will present new results from the ongoing Hyper Suprime Cam survey currently being carried out by Subaru. The HSC survey is an unprecedented effort to map 1400 deg^2 in 5 bands to i~26. This unique combination of depth and area enables us to study the individual light profiles of several thousand super massive galaxies (M*>11.6 Msun) to 100 kpc and beyond. We show that massive galaxies are not self similar and that instead their light profiles are diverse. This diversity is not random: using weak gravitational lensing we make a remarkable discovery. There is a tight correlation between the shapes of galaxy light profiles and their host dark matter halo mass. Deep imaging is critical for measuring the total light from these galaxies. With better luminosity measurements in hand, I will show that there is a much tighter relation between the luminosities of super massive galaxies and dark matter halo mass that previously recognized. Finally, I will discuss how our results have the potential to transform optical galaxy cluster detection and the way we use cluster surveys to constrain dark energy.