Hidden Depths in the Local Universe: the Stellar Stream Legacy Survey
  Mergers and tidal interactions between massive galaxies and their dwarf
satellites are a fundamental prediction of the Lambda-Cold Dark Matter
cosmology. These events are thought to provide important observational
diagnostics of nonlinear structure formation. Stellar streams in the Milky Way
and Andromeda are spectacular evidence for ongoing satellite disruption.
However, constructing a statistically meaningful sample of tidal streams beyond
the Local Group has proven a daunting observational challenge, and the full
potential for deepening our understanding of galaxy assembly using stellar
streams has yet to be realised. Here we introduce the Stellar Stream Legacy
Survey, a systematic imaging survey of tidal features associated with dwarf
galaxy accretion around a sample of ~3100 nearby galaxies within z~0.02,
including about 940 Milky Way analogues. Our survey exploits public deep
imaging data from the DESI Legacy Imaging Surveys, which reach surface
brightness as faint as ~29 mag/arcsec^2 in the r band. As a proof of concept of
our survey, we report the detection and broad-band photometry of 24 new stellar
streams in the local Universe. We discuss how these observations can yield new
constraints on galaxy formation theory through comparison to mock observations
from cosmological galaxy simulations. These tests will probe the present-day
mass assembly rate of galaxies, the stellar populations and orbits of
satellites, the growth of stellar halos and the resilience of stellar disks to
satellite bombardment.
