The remnants of galaxy formation from a panoramic survey of the region around M31

Understand

In hierarchical cosmological models, galaxies grow in mass through the continual accretion of smaller ones.

• The tidal disruption of these systems is expected to result in loosely bound stars surrounding the galaxy, at distances that reach $10 - 100$ times the radius of the central disk.
• The number, luminosity and morphology of the relics of this process provide significant clues to galaxy formation history, but obtaining a comprehensive survey of these components is difficult because of their intrinsic faintness and vast extent.
• Here we report a panoramic survey of the Andromeda galaxy (M31).