  We study numerically the phases and dynamics of a dense collection of
self-propelled particles with soft repulsive interactions in two dimensions.
The model is motivated by recent in vitro experiments on confluent monolayers
of migratory epithelial and endothelial cells. The phase diagram exhibits a
liquid phase with giant number fluctuations at low packing fraction and high
self-propulsion speed and a jammed phase at high packing fraction and low
self-propulsion speed. The dynamics of the jammed phase is controlled by the
low frequency modes of the jammed packing.
