ALMA Observations

The dynamical evolution of planetary systems leaves observable signatures in debris disks. Optical images trace micron-sized grains, which are strongly affected by stellar radiation and need not coincide with their parent body population. Ob-servations of mm-size grains accurately trace parent bodies, but previous images lack the resolution and sensitivity needed to characterize the ring’s morphology. Here we present ALMA 350 GHz observations of the Fomalhaut debris ring. These observations demonstrate that the parent body population is 13-19 AU wide with a sharp inner and outer boundary. We discuss three possible origins for the ring, and suggest that debris confined by shepherd planets is the most consistent with the ring’s morphology. Subject headings: Planet-disk interactions — planetary systems — Submillimeter: planetary systems 1