Why do galaxies die?

Surveys of the distant universe show that star formation in very massive galaxies begins to die out nearly 10 billion years ago. This mysterious trend continues to the present day, affecting lower mass galaxies with time. Unfortunately, the physical origin of “quenching” as well as how quenched galaxies maintain quiescence remains unknown, with ongoing confusion surrounding various proposed mechanisms. To make progress, we must resolve the internal signatures of the processes that end star formation. In the second half of this talk, I will describe a new Sloan Digital Sky Survey designed to do exactly that. MaNGA (Mapping Nearby Galaxies at APO) began on July 1st and will obtain resolved spectroscopic measurements for 10,000 galaxies, providing valuable maps of quenching patterns, gas flows, and stellar dynamics that can discriminate the physics behind galaxy death. I will present early evidence from MaNGA for a new class of phenomena we term “red geysers” that may play a key role in preventing star formation in quenched galaxies.